1 lb. lean ground beef
1 sm. onion, chopped
1 pkg. (1 1/4 oz.) taco seasoning mix
1 1/2 c. shredded Cheddar cheese, divided
10 taco shells
2 c. shredded lettuce
2 med. tomatoes, chopped

Crumble beef into 2 quart microproof casserole. Add onion. Microwave on High 2 1/2 minutes. Stir to break up beef. Cook on High 3 1/2 minutes more. Stir beef; drain. Stir in seasoning mix. Stand taco shells in large, shallow microproof baking dish. Divide beef mixture among shells. Top each with 1 tablespoon of the cheese. Cook on High 2 1/2 minutes.

Top each with lettuce, tomatoes and rest of cheese.