In a skillet over medium heat, cook the beef and onion until evenly browned.
Remove the tops, seeds, and membranes of the bell peppers. Chop the tops and throw in with the onions and beef. Arrange peppers in a baking dish with the hollowed sides facing upward. (Slice the bottoms of the peppers if necessary so that they will stand upright.)
In a bowl, mix the browned beef, onion, chopped peppers, cooked rice, 1 can tomato sauce, Worcestershire sauce, garlic powder, onion powder, salt, and pepper. Spoon an equal amount of the mixture into each hollowed pepper. Mix the remaining tomato sauce and Italian seasoning in a bowl, and pour over the stuffed peppers.
Cover with aluminum foil and bake for 30 minutes in the preheated oven. Remove peppers from oven and top with cheese (mozzarella or cheddar) and return to oven for about 10 minutes