Preheat oven to 350°F. Stir Sauce Mix, water and tomato sauce in medium saucepan. Bring to boil. Reduce heat and simmer 5 minutes or until thickened, stirring occasionally.
Brown meat in large skillet on medium-high heat. Drain fat. Stir in beans, corn and 1/2 cup of the sauce.
Cover bottom of greased 13x9-inch baking dish with 4 of the tortillas. Layer with 1/2 each of the sauce and filling mixture, and 1 cup cheese. Repeat layers with remaining tortillas, sauce, filling and cheese.
Bake 20 minutes or until heated through. Serve with desired toppings.