I once made a stuffed tomato recipe from The Two Fat Ladies. I can't
remember what they were stuffed with but I used yellow and red tomatoes and
baked them in the oven. I sometimes do stuffed peppers. I normally use rice
and beef with tomato sauce on top. But my former FIL wouldn't eat rice so I
made some for him with mashed potatoes inside and topped them with tomato
sauce and cheese. They were very good.

I think I have seen recipes for stuffed onions. And my former SIL used to do
stuffed zucchini. Not sure I could find any in the stores that is big enough
for stuffing. She used those whoppers that people grow in their gardens and
always seem to have an excess of. She never used recipes. Just threw things
together. But IIRC, she did them like you would the peppers. And of course
there is stuffed cabbage. I may have made that once. IIRC, it was rather a
pain to make.

Are there any other veggies you can stuff and bake in the oven? I am wanting
to use a grain like barley or rice and a protein like cheese, beans or meat.

Yes, I know there are cold stuffed veggies as well. But it is really cold
here right now and no end in sight so I am wanting to keep the oven on. Any
suggestions?