Preheat the oven to 400 degree F. Lightly coat a 2-quart square baking dish with cooking spray or grease with shortening. Prepare corn muffin mix according to package directions. Spread corn muffin batter evenly in prepared dish. Bake in the 400 degree F oven for 18 to 20 minutes or until corn-muffin layer is done.
Meanwhile, in a medium skillet brown meat. Drain fat. Stir in taco sauce. Heat through. Spoon over muffin layer in baking dish. Sprinkle cheese over meat. Return to oven. Bake for 1 to 2 minutes more or until cheese melts.
Serve topped with lettuce and additional taco sauce or salsa, if desired. Makes 6 servings.