Preheat oven to 375F
Heat large skillet on medium high heat. When pan is hot, add meat. Brown meat stirring occasionally and breaking up clumps into smaller pieces. Cooking should take 7-8 minutes. Add to large bowl when done cooking
Mince onions and garlic. Using the same skillet as before on medium high heat, add onions. Cook until onions start to turn translucent, about 5-6 minutes. Add in garlic and cook for an additional 2-3 minutes, then pour onions and garlic into the large bowl with the browned meat. Do not let the garlic burn, if it starts to turn brown stop cooking and add the cooked onions and garlic to the meat bowl. You can optionally cook one cup of chopped portobella mushrooms along with the onions.
Add remaining ingredients to the bowl, minus the green and red peppers and the tomato sauce. Mix well.
Cut the tops off of the green and red peppers, remove seeds. Place peppers in baking dish. Scoop meat mixture into the now hollow peppers. Cover the top of the peppers with tomato sauce. Cover and cook in oven for 45 minutes.