The only way Timber will eat raw vegetables is if they are hanging on his skewer. They make a metal rod which screws into a holder which hangs in the cage ("skewer"). He seems to like it's swinging motion and pecks at the vegetables. Not sure how much he is eating, but I know he gets a little that way. I really had to do a lot of experimenting to find anything he liked. You also have to keep offering things that are good for him. Like toddlers, one day they will eat it and another they won't. You might try cooked sweet potato in his bowl, that is one Timber will eat a bit of. You might try offering it to him on a spoon first. Timber likes his a bit warm but not hot. For some reason, probably his handfed history, Timber will try just about anything I offer on a spoon. It may end up on my face if he doesn't like it and gives the beak shake, but at least he will try it. Another thing to try is to thread raw and well washed greens (like Kale) through the cage bars. Whether it is just because he doesn't want them on his bars or because he likes them, he will usually pull it out, getting some in his beak as a result.
Remember that grey's are foragers by nature. Most of them love boxes and paper sacks. I put a box or sack (make sure you remove any tape) in the bottom of his cage. I put shredded paper and other safe stuff in there, along with things like a cracked walnut (I have to get it started or he won't crack it) or other items I want him to try in there. He loves to root around in the box, chew on it, and look for the stuff hidden there. There are all sorts of foraging toys you can buy, but Timber's favorite is still the box or sack. He loves corrugated cardboard like shipping boxes, and will spend hours shredding it into fine bits.
As Ray said, you need to try some pellets and keep the fruit consumption low. You can also give him the whites from boiled eggs (I give Timber a little yolk as well but not much) and boiled chicken wings.
There are several threads about diet you may want to check out. When it comes down to it, each bird is different in their likes and dislikes. You just have to keep experimenting until you find a balance!