I use pine nuts and pumpkin seeds as treats, but I only give her treats very occasionally, like during training. Or in her foraging toys.
It's best to continue to give your bird what it was already eating, if it likes it. Originally, Quincey was on Tropican, but it wasn't the best. The vet gave me samples of better foods for her to try (including Lafeber and Harrison's), to see if she would like one of them better. If she didn't, then we would stay on Tropican. As soon as Quincey tasted Harrison's, she shunned her regualr food. So we switched to Harrison's, which is the best alternative, according to my vet. I'm happy that we stopped Tropican, it smelled like bubblegum!
I also give tonnes of veggies and fruit as well. Her favourites are blackberries, strawberries, kale, peas, carrots, sweet potato (cooked and mashed), and orange pepper.
Look on the internet, there are lots of sites that tell you which veggies and fruit are best to give.