1Heat oven to 400°F. Spray 13x9-inch (3-quart) glass baking dish with cooking spray. In 10-inch skillet, cook beef, onion and salt over medium-high heat, stirring frequently, until beef is brown; drain. Spread in dish. Top evenly with frozen mixed vegetables.
2In medium bowl, stir Bisquick mix, milk and eggs with wire whisk until blended. Pour into baking dish.
3Bake 30 minutes. Sprinkle evenly with cheese; bake 10 minutes longer or until knife inserted in center comes out clean. Cut into squares.