Meanwhile, cut peppers lengthwise and clean out seeds & membrane.
Add undrained tomatoes, boca crumbles and rice to softened onion mixture. Simmer until well combined. Add ketchup and mustard **NOTE** Add more or less depending on how thick/thin sauce is. It should be just thick enough to remain in peppers. Play with it and add it to taste!
Put pepper shells in a 13x9 and spoon mixture into peppers and cook covered with foil for 1 to 1 1/2 hours at 350°F or until peppers are soft.