Cook and stir meat and onion in skillet until meat is brown. Drain off fat. Stir in tomato sauce, garlic salt, chili powder and pepper; simmer uncovered 15 minutes.

While Meat Filling is simmering, Heat taco shells as directed on package. Spoon Meat Filling into taco shells. Top filling with cheese, lettuce and tomato. If desired, serve with taco sauce.