Heat oven to 400°F. Spray 8-inch square (2-quart) glass baking dish with cooking spray. Sprinkle 1/4 cup of the cheese in baking dish. Top with zucchini, corn, tomato and onion. Sprinkle remaining 1/4 cup cheese over vegetables.
In small bowl, stir remaining ingredients until blended. Pour over vegetables and cheese.
Bake uncovered 32 to 35 minutes or until knife inserted in center comes out clean. Let stand 5 minutes before cutting.