I'm having a similar experience introducing new foods to my almost-8-month-old Quaker parrot Ralph. He's a little reluctant to accept unfamiliar things as actually being food, and, since he is a Quaker, he tends to be a little stubborn about it. So you do have to be persistent, even to the point of offering previously rejected foods over and over again. Try feeding the fruits and vegetables in different forms, both raw and cooked. Ralph likes a lot of things if they're finely chopped, but won't touch a larger piece of the same food (apple and banana, for example).
A lot of parrots like air-popped popcorn (without oil, butter or salt). Different types of nuts can be given as an occasional treat too (they're another high-fat food and shouldn't be fed too often). Ralph likes a little bit of cheese too, the same extra-sharp Cheddar I eat. He's also very fond of cinnamon toast; cinnamon is good for birds, and if the toast is whole-grain rather than white bread, it's more nutritious. I have no problem with giving a parrot a few treats that are just fun for them to eat-- things like a very small morsel of vanilla cake or oatmeal cookie. As long as the parrot has a basic diet that is nutritious, and the bird is in good health, that kind of treat in moderation shouldn't do any harm (the key is to feed only small amounts and not too often). I had a happy, healthy Amazon parrot who enjoyed that sort of treats and he lived to a ripe old age.
