Add the rest of the ingredients to a sauce pan. Heat until warmed through. You will want to judge the amount of liquid from the tomatoes you use. The mushrooms with soften in the liquid. You don't want soup, but you don't want a dry mixture either.
Add in the rice.
Cut the tops off your whole bell peppers and stuff. I crumpled foil in the bottom of my pan to help the peppers stay upright. Bake for about 45 minutes at 350.