1Heat oven to 375°F. Generously spray bottom and sides of 15x10x1-inch pan with cooking spray. In 12-inch skillet, cook beef and onions over medium heat, stirring occasionally, until beef is thoroughly cooked; drain. Stir in soup, vegetables and milk.
2In large bowl, stir Bisquick mix and water until moistened. Spread evenly in pan. Spread beef mixture over batter. Sprinkle with cheese.
3Bake uncovered 35 minutes.