Heat oven to 400ºF. Spray 13x9-inch pan with cooking spray.
Stir Bisquick mix, water, salt, eggs and 1 cup of the cheese in medium bowl; spread in pan. Mixture will pretty pretty thick.
Cook beef ketchup and onions in 10-inch skillet over medium-high heat 5 to 7 minutes, stirring occasionally, until brown; drain. Stir in soup and vegetables; heat until hot (mixture will be thick) Spread over batter in pan.
Bake 23 to 25 minutes or until edges are light golden brown.
Sprinkle with remaining 1/2 cup cheese. Bake 1 to 3 minutes longer or until cheese is melted.