In large skillet, cook ground beef, chopped onion, and chopped green pepper until meat is no longer pink; drain off fat. Stir in tomatoes, salt, and garlic powder. Simmer, uncovered, for 10 minutes, stirring frequently.
Cut cabbage into 6 wedges. Cook cabbage in a small amount of boiling salted water, covered, for about 10 minutes and drain well. Arrange cabbage wedges in a lightly buttered 9-inch square baking dish. Pour ground beef mixture over and around the cabbage wedges. Bake cabbage casserole, uncovered, at 350° for 20 to 25 minutes. Sprinkle cheese over cabbage casserole and bake about 5 minutes longer.