I like the idea of stuffed peppers, but add a lot of chopped mushrooms to the rice before stuffing. Smother with an alfredo or other cheesy sauce, and cook in the smoker.
Or, scrape the gills from some portobello mushrooms, sprinkle the cavity generously with grated cheese, and smoke them. Once done, add some (VERY well drained) cooked chopped spinach on top of the cheese, top with a poached egg, and cover with Hollandaise sauce. Essentially a smoker based vegetarian variation on eggs benedict.
Quiches are also vegetarian friendly, and could probably be cooked in the smoker.