Preheat oven to 350
In a large pot over medium heat the olive oil, onion, garlic and add the butter. Once the garlic is golden, remove and discard.
Add the ground beef to the large pot. With the back of a spoon break down the ground beef on smaller pieces. Cook until all the juices from the meat are gone.
Add the tomato sauce, salt and pepper. Lower the heat, cover and cook for 20 minutes.
Meanwhile slice the bell peppers in half lengthwise. Remove all the internal seeds. Clean and dry. Sprinkle with salt and pepper.
Butter an ovenproof pan.
When the tomato sauce is done, add the rice and mix well. Add the parmesan cheese and mozzarella to the mixture.
Fill each half of bell peppers with tomato and rice. Sprinkle the remaining 2 tablespoons parmesan cheese over the peppers.
Bake in the hot oven for 20 to 25 minutes, until cheese is melted, and the peppers are slightly soft.