Slice off the stem end (top) of the peppers and remove all seeds and bitter white filament. Boil peppers and their tops 2 minutes in lightly salted water. Remove from boiling water and dip in ice water to stop cooking process. Drain on paper towels and set aside. Mince onion and saute until soft in 1 tablespoon olive oil. Add ground beef and cook on medium heat until hamburger looses its red color. Drain off grease and combine with cooked rice and 12 ounces of the tomato sauce. Allow to cool. Add grated cheddar cheese and salt and pepper to taste. Spray a baking dish with non-stick spray. Place peppers in baking dish and stuff with hamburger mixture. Pour remaining tomato sauce over top. Replace pepper tops. Cover dish with foil and bake in 350 degree oven approximately 45 minutes.