Heat oven to 400°F.
In 10-inch skillet, cook sausage, onion, bell pepper and garlic over medium heat 8 to 10 minutes, stirring frequently, until sausage is no longer pink; drain. Stir in tomato sauce, corn and mushrooms. Heat to boiling; remove from heat.
In medium bowl, stir all topping ingredients except cheese. Beat vigorously with spoon 30 seconds. Stir in cheese.
Spoon sausage mixture into ungreased 2-quart casserole. Pour topping over hot sausage mixture, spreading evenly.
Bake uncovered 20 to 25 minutes or until topping is golden brown.