Add rice and 1 cup water to a small sauce pan. Bring to a boil. Cover and let cook 20 minutes.
While rice is cooking, heat oil in medium skillet. Add onion. Cook until soft and browned, about 7 minutes, stirring occasionally. Add garlic. Cook another 2 minutes.
While onions are cooking, pulse sausage in a food processor until it resembles crumbled meat. Place in a medium bowl.
Add onion and garlic mixture to bowl. Add cooked rice, diced tomatoes, salt, and pepper. Stir well.
Place peppers cut side up in 2 baking dishes. Stuff with sausage mixture. Top with cheese, if using.
Bake at 350 30 min or until hot and cheese is melted.