Cut the tops off the bell peppers and remove the seeds and membranes. Chop the pepper tops and set aside.
In a large bowl, combine the ground beef, cooked rice, diced tomatoes, chopped onion, chopped pepper tops, garlic powder, oregano, salt, and black pepper. Mix well.
Stuff the pepper halves with the meat mixture.
Place the stuffed peppers in a baking dish. Add about 1/2 inch of water to the bottom of the dish.
Cover the baking dish with foil and bake for 30 minutes.
Remove the foil, top with cheese if desired, and bake for another 10-15 minutes, or until the peppers are tender and the cheese is melted and bubbly.
Let stand for a few minutes before serving.
Notes
These stuffed peppers are great on their own or served with a side salad.