Heat oven to 350 degrees. Cook ground beef and onion until beef is brown; drain. Spoon into ungreased 13x9x2" baking dish. Stir in taco seasoning mix (dry), tomato sauce and corn. Sprinkle with cheese.

Stir remaining ingredients until blended. Pour over beef mixture.

Bake 35 min or until light golden brown. Serve with sour cream, chopped tomato and shredded lettuce if desired.