Heat oven to 400 degrees. Generously grease 13x9x2" baking dish. Cook beef and onion in 10" skillet until beef is brown; drain. Stir in soup, vegetables and milk. Stir baking mix and water in baking dish until moistened; spread evenly. Spread beef mixture over batter; sprinkle with cheese. Bake 30 minutes. 8 to 10 servings.