Heat large skillet over medium heat; crumble beef into skillet and cook, stirring 7 minutes or until no longer pink; pour off drippings. Add onion and cook until tender. Add soups and 1/2 soup can of water.
Line bottom of 9x13-inch baking dish with 4 tortillas, torn into pieces. Layer with 1/2 meat mixture, 1/2 chilies and 1/2 cheese. Layer one more time. Bake in preheated 325°F oven 45 minutes or until hot and bubbling. Top with shredded lettuce, chopped tomatoes and sour cream, if desired.