Preheat oven to 375°F. Grease 11 x 7-inch baking dish. Cook beef and onion in large skillet over medium heat, stirring occasionally, until beef is browned. Drain and discard excess fat. Stir in taco sauce, water, chiles, and seasoning mix; bring to a boil. Reduce heat to low. Cook 3 to 4 minutes, stirring occasionally. Layer half of broken taco shells on bottom of prepared baking dish. Cover with half of meat mixture; sprinkle with 1 cup cheese. Repeat layers with remaining ingredients. Bake 20 to 25 minutes or until bubbly and cheese is melted. Serve with desired toppings. Makes 8 servings.