Cut the tops off the peppers and remove the seeds. Place the peppers in a large saucepan and cover with water. Bring to a simmer and cook 3 minutes, just until the peppers are slightly soft. Drain, rinse with cool water and set aside on paper towels to drain.
In a skillet, heat the ground beef and onion and cook until no pink remains. Drain.
Add the salt, pepper, rice, garlic powder and half of the tomato sauce.
Stir well and spoon into the peppers.
Top with the other half of the tomato sauce.
Bake in an ungreased dish at 350 for 25-30 minutes. Serve warm.