In a large mixing bowl combine egg, onion, 1/4 cup salsa, the chili powder, garlic, and salt; add ground beef and mix well.
Shape into a ball and place in a 9-inch pie plate. Flatten meat mixture to a 6-inch circle; set aside.
Prepare corn muffin mix according to package directions. Spread corn muffin batter over meat mixture in pie plate. Bake about 50 minutes or until an instant-read thermometer inserted into the meat loaf registers 160F. Remove from oven.
Halve cheese slices and arrange on top of the corn muffin mixture. Cover loosely and let stand 10 minutes before serving. If desired, serve with additional salsa. Makes 6 servings.