1) Core peppers by removing stem and then scooping out interior, removing all the white pith and seeds. Parboil for 3 minutes in boiling water; remove, rinse in cold water and drain. 2) Heat oil in frying pan, add Onion, fry 2 minutes. Add zucchini, fry another 3 minutes. Add Mushrooms, fry another 1 minute, drain [this is to keep the filling from being soupy; you may want to try just sauteing until the liquid is gone]. Add rest of ingredients, with salt and pepper to taste. Combine thoroughly. 4) Bake at 350 degrees for 30–45 minutes, or until the peppers are tender. Serve hot.