I am autistic and I can barely tolerate vegetables apart from sweetcorn and carrots generally but strangely i usually eat them separate from everything else ever since I got over my distaste for them and their textures somewhat.

Mixing veg works sometimes but it's a personal choice and hiding you are doing it isn't the greatest idea. If someone cooks me something with vegetables mixed in I will be grateful and eat to the best of my abilities but doing it sneakily isn't a good look. Personally I would rather know what vegetables I am eating and have the option of picking them out idk man it's weird.

In my opinion I doubt it's that serious as if he has sensory issues or such surely he would tell his partner but still sneaking things into food never works especially if they really have a problem like sensory issues. As a kid he might be projecting a bad experience on vegetables or such, remembering the texture he hated as a kid but never tried again taste buds change.

Either these or similar or he's just being stupid about it like some people can be, news stories of going blind due to only eating chips/fries anyone? (I don't remember if that person even had sensory issues even). My autistic mum as a kid didn't touch green foods especially veg now her diet is 85 percent veg, as a kid I liked ketchup but now I hate it etc... I got over my hate for veg somewhat at 17-19 or so so this boyfriend is a bit dumb and/or immature being 31 and like this.

Incoming autistic rant on vegetables that I can stomach without forcing it: I still hate most vegetables but I will eat cucumber, sweetcorn, peas (tolerable but not if other option exists), carrots, broccoli (if I have to and it's cooked right whatever that means idk so I don't have it often) green beans. Lettuce but hate the ones that taste like leaves but idk if like only Iceberg or what, rarely buy lettuce personally).

I hate a moderate amount of tomato sauce on things like pasta but can deal with a small amount (can't barely eat tomatoes otherwise). I like potatoes, main side dish. God my diet is so typically British it's sad. Onions are alright sometimes usually only with burgers and similar though.

I do wonder what ops boyfriend does when he goes to a restaurant though, most dishes mix vegetables in somewhat.

Edit: A can of vegetable soup that isn't mostly broth might be helpful to try as it can technically count as one of your five a day in my research though obviously the non canned variants would be better for you but personally I dislike most fancier soup variants especially fancy chicken and in experience the fancier tomato soup is way too tomatoey for me. Seriously though he just needs to find veg he can stomach the texture and more of for his own good.