Birds bodies are designed and created to eat seeds, nuts, legumes, grains, etc. They need to eat seeds every day to keep their GI Tracts healthy, and to stimulate their foraging instincts and to use their beaks to "shell"...Pellets are wonderful and should be the main "staple" of your bird's daily diet. However, Pellets do not exist in nature, and pellets will not fulfill all of your bird's daily physical or mental needs. So the goal is to have your bird eating a healthy, fortified Pellet as the main staple of his diet, along with a small amount of a healthy, low-fat, varied seed mix, along with fresh veggies and dark. leafy greens every day.
We get into trouble with the seed-mixes when we buy ones that contain either sunflower seeds or nuts, usually it's peanuts that the junk seed-mixes are full of, but your bird's seed-mix should not contain ANY type of nuts, sunflower seeds, or corn. You need to find a healthy, varied seed-mix that contains NO sunflower seeds and NO nuts or corn at all. So the one you are feeding him is not good if it contains nuts, as they are loaded with fat. Nuts, just like sunflower seeds, should only be given occasionally as special treats or training rewards, and that's it, not a part of their daily diet. So you need to look for a better seed-mix, such as Roudybush, Tropimix, Higgins Vita Seed with no Sunflower seeds, Higgin's VitaSeed California Blend, Sunseed no sunflower mix. There are others, but these are some of the best, as they contain no nuts, no sunflower seeds, and contain lots of different whole-grains, legumes, low-fat seeds, veggies, etc.
****Also, you do not want to feed your bird Fruit every day either. We often lump fresh fruit in with fresh veggies, like it's an "either-or" situation, but that's not the case at all. While fruit contains many healthy vitamins and minerals for our birds, unfortunately it is absolutely loaded with sugar. And even though it's "natural" sugar, it ends-up being turned-into fat and stored in their livers just like the fat from the sunflower seeds and the nuts does. So fresh fruit should only be given to your bird at most 3-4 days a week, and in small portions.
You want to feed your bird lots and lots of fresh veggies however, and if you don't feed him the fruit as a part of his regular, daily diet, he'll be much more likely to eat his fresh veggies....A lot of people say "My bird hates veggies, he just won't eat them", but then we find out that they are feeding their bird fresh fruits along with the veggies, which totally explains why they won't eat the veggies, because they only want the sweet, sugary fruit!
You can basically feed your bird ANY fresh veggie and any dark, leafy greens every single day, and lots of them! (EXCEPT for onions/leeks, as they are toxic to birds, and any of the Iceberg or "watery" lettuces, as they contain no nutritional value). You can also try making different "Chop" recipes consisting of several different types of fresh veggies to see what he likes.
So he needs to get his pellets as the main staple (he will eat his pellets if you ONLY provide him the pellets as his food throughout the day, he won't purposely starve himself, I promise). We are the reason that our birds refuse to eat pellets, fresh veggies, etc. It's no different than feeding our young human children. Of course they want the cookies and candy and ice cream and not the good foods, but we would never give-in and just feed them the crap instead of their real foods (well, most people don't, lol).
****Here's what I do with my Cockatiel, who was my one bird who just would not transition from a crappy seed-mix to a pellet and a healthy seed-mix with veggies:
First, find a healthy, low-fat, varied seed-mix that contains NO sunflower seeds and NO nuts at all. Ditch the crappy seed-mix with the nuts. My stubborn Cockatiel loves the Tropimix and the Higgin's VitaSeed California Blend, both of which you can buy at any Petco. I guess you already have a pellet that you've chosen, and make sure that you have a nice variety of fresh veggies at home and that you chop them up into very small pieces, as usually the smaller the bird, the smaller they like their veggie chop. I give my birds their small amount of healthy seed-mix first thing every morning, and get it out of the way. They each only get about 1/4 cup of healthy seed mix each day, that's it, no more. It's going to look like it's not enough, but remember, that's only a small part of their daily diet...
So first thing in the morning I give them their very small amount of healthy seed-mix, which they typically gobble up right away. Then before I leave for the day I put their pellets in their bowls for the day. That's all they are going to have to eat all day long, so trust me, they'll eat them, as they've already devoured their healthy seed-mix, and they're going to get really hungry right around early afternoon. ****Something that you need to make sure of is that the SIZE of the pellets you are feeding is correct for your bird. I don't know what brand/type of pellets you're feeding your Green Cheek, but you need to make sure that his pellets are small enough for him, as sometimes they don't like to have to hold their pellets if they are quite large. I feed Tropican pellets to my birds, and my Quaker, Green Cheek, and Cockatiel all eat the small "Conure" formula, where the pellets are about the size of a popcorn kernel; however, my Senegal parrot, who also eats Tropican pellets, won't eat the same size that the other do (of course, lol), so for him I have to buy the next size up of the Tropican pellets, which is meant for "medium parrots and Amazons". My Senegal likes to be able to hold his pellets in his foot and eat them that way, rather than putting a small pellet in his mouth all at one time. They're all different in what they like, so sometimes you have to try different things. I used to feed Zupreem Natural pellets to all of my birds, and it was the same way, the 3 smaller birds at the Zupreem Natural pellets that were about the same size as the Tropican they eat now, and the Senegal would only eat the much larger Zupreem Natural pellets for Amazons. So it might take some experimenting, just like the fresh veggies will...
So they get their very small portion of healthy seed-mix first thing in the morning (and it's soooo important that you ONLY give your bird a very small portion of whatever healthy seed-mix you choose, 1/4 cup at most, even if it looks like it's not enough, because if you feed him any more seed-mix, he won't need to eat his pellets)...Then I put their daily portion of pellets in their bowl and they have them for the day. When I get home and I'm ready to make and eat my dinner, that's when they get their fresh veggies, and they always eat dinner WITH me. They see me eating my dinner and they want to eat their dinner at the same time, and this will also serve to encourage them to eat more of their fresh veggies. Now I make-up large batches of different fresh veggie "Chop" mixes every Sunday, put single-portions into little plastic baggies, and put the baggies in the freezer, so that they will keep for as long as I want them to. Then each morning before I leave, I take out the baggies that they will eat for that particular day, and put them into the fridge to thaw-out, and by the time I get home for dinner, they are thawed-out and ready to go. So I make my dinner (with them in the kitchen with me, playing on their T-Stands), and then I get out their portions of fresh veggie Chop mixes, put their fresh veggies in their bowls, and we all sit down and eat dinner together. It also helps if you put some of the exact same fresh veggies that you have given them onto your plate too, so that they think you are eating the same thing that they are, this usually encourages them to eat the veggies because they always want what you have. They typically eat their fresh veggies right away, and then since I'm still eating my dinner, they will also finish-off any remaining pellets that they have left in their dishes.
Now I give my guys a small amount of fresh-fruit 3-4 days a week, but they know that they aren't going to get any fresh fruit unless they have finished all of their pellets for the day. It took a while to get them to do this, but now I have no issues with their pellets at all, they are usually all gone by the time I get home in the late afternoon. You absolutely do not want to give them fresh fruit every single day in large amounts, but what I do is that 3-4 days a week they get a small piece of fruit, whatever it is for that day, and they get that after they finish their fresh veggies. But it's a very small piece of fruit, not nearly even close to the amount of fresh veggies they get. If you feed your bird fresh fruit in the same amounts that you do their fresh veggies, then they are not only going to stop eating the veggies and just want the fruit (much like they will stop eating their pellets if you feed them large amounts of seed-mix), but they will also eventually develop Fatty Liver Disease, Diabetes, and become overweight, which then causes severe Arthritis in their joints, along with the formation of many Lipomas all over their bodies (parrots are extremely prone to developing Lipomas, which are fatty tumors that are basically just balls of fat depositing under their skin due to them eating too much fat, sugar, etc.).
