Katherine, do you have any of the Moosewood cookbooks? (Or could you find them in a local library?) I've got a stack of them (I like vegetarian cooking), and there are a lot of possibilities.
Chilean Squash (cooked squash or pumpkin, onion, red & green bell peppers, garlic, cumin, eggs, corn, chili powder, cheddar cheese, coriander, salt, and a tiny bit of cayenne and black pepper) sounds kind of like what you're looking for... if he eats eggs?
There are a lot of different vegetarian stew possibilities, and also vegetarian versions of shepherd's pie, that are pretty good and might be Thanksgiving-ish enough.
I once made vegetarian spanikopita for Thanksgiving. It was a lot of work.