Cook first 3 ingredients in a large skillet over medium-high heat, stirring until beef crumbles and is no longer pink. Drain well.
Place beef mixture in a large bowl. Stir in tortilla pieces, next 4 ingredients, and 1 cup cheese; spoon mixture into a lightly greased 11- x 7-inch baking dish. Sprinkle evenly with remaining 1 cup cheese.
Bake at 400° for 20 to 25 minutes or until bubbly. Serve casserole with desired toppings.