1 lb. lean ground beef
1 med. onion, chopped
1 stalk celery, chopped
1 can (8 oz.) tomato sauce
1 tsp. prepared mustard
1 tsp. chili powder
4 hamburger buns, split
1/2 c. (2 oz.) Colby cheese, shredded

Combine beef, onion and celery in 1 1/2 quart microproof casserole. Cover with casserole lid and cook on high, 5 to 7 minutes, stirring once. Stir in tomato sauce, mustard, and chili powder. Cover and cook on 80% power, 3 to 5 minutes. Spoon over buns. Sprinkle with cheese.