Preheat oven to 400 degrees F. Spray a 12 x 8-inch baking dish with nonstick cooking spray. Stir together corn muffin mix, milk, egg substitute and oil. Spread in bottom of prepared dish.
In a large skillet, cook ground beef and onion over medium-high heat until beef is lightly browned, stirring to break up meat; drain fat. Stir in corn.
Stir together undrained tomatoes and cornstarch, breaking up any large pieces of tomato. Stir into beef mixture. Bring to a boil, stirring frequently.
Spoon beef mixture over cornbread mixture. Cover with foil. Bake 15 minutes. Uncover, bake 10 additional minutes. Sprinkle with cheese. Return to oven, bake 2 to 3 minutes or until cheese melts. Let stand 5 minutes. Cut into squares.