1Heat oven to 450°F. Generously spray 13x9-inch (3-quart) glass baking dish with cooking spray. In medium bowl, stir Bisquick mix, Italian dressing and 3 tablespoons milk until soft dough forms. Pat dough on bottom of baking dish. Bake 8 minutes. Cool completely, about 45 minutes.
2Sprinkle vegetables over baked crust. In medium bowl, beat remaining ingredients except cheese with wire whisk or fork until blended. Pour over vegetables. Sprinkle with cheese. Cover; refrigerate at least 2 hours.
3Heat oven to 350°F. Cover with foil; bake 30 minutes. Uncover dish; bake 40 to 50 minutes longer or until knife inserted in center comes out clean. Let stand 10 minutes.