Timber is a very picky eater. He doesn't care for fruit either, except for sharing a bite of dad's banana once in awhile. I don't mind, because greys aren't supposed to have a lot of fruit anyway. As luvparrots said, veggies are important. Sometimes you can hide them in things they do like (like you would with a toddler). Sometimes it is a matter of finding some Chicken likes. It takes some experimenting, and sometimes it takes several times of offering the same thing before they give it a try. For instance, Timber will eat peas in the pod (not snow pea pods but real peas) if I put them on the skewer in his cage raw. He will only eat sweet potato if it is cooked and mashed. Carrots and broccoli are a "sometimes" thing on the skewer (raw, won't eat cooked). I found that he loves artichokes. I buy fresh ones, cut off the stem plus about a half inch on the stalk end and a half inch off the top, strip the outer leaves (mostly to help get rid of pesticides) and toss it in the bottom of the cage after washing well. He will chase and chew on that artichoke all day long, leaving only pieces of the leaves at the end of the day.
I'm just trying to emphasize that you may have to try a variety of things before you find what he likes.
What ever you try, make sure to wash properly to get rid of pesticides, which are lethal to birds.