OK, my son has Aspergers and this sounds very familiar behaviour -- not saying your DSS does, but the same strategies might help IF it's something he wants to overcome. I'd start by assuming that he does and that it could take a LONG time to sort out.
DS hates/hated 'mixed' food and certain textures mashed potato, chopped carrot, cooked apple, for instance. He's also very sensitive to taste, but it's the texture that would make him flee the room gagging. We had to go at it very slowly get his agrrement to try one new food, meaning he might touch it or have it on his plate; then another time he'd lick it; maybe a nibble next time; etc. We also worked from things he did eat and moved slowly into healthier versions (crisps to potato slices to roasties to baked potatoes took nearly a year!)
Gradually the gag reflex didn't happen so often, and he'll now just scrape sauce off food rather than needing a separately cooked meal (still drives me potty, but hey).
He'll eat things raw or barely cooked that he can't tolerate stewed or mushy.
Can you ask your DSS first which foods bother him most and why? Then see if he'll agree that the situation does need some tweaking, and that he'll find it useful later on if he gradually increases his range of tolerance. I'd start then with whichever fruit/veg he finds least revolting -- he and you need some success to build on. If he can now touch fruit and couldn't before, that's already a successful change, so don't knock it.
I seem to be writing you an essay. Sorry, and good luck!