Preheat oven to 350°. In a large skillet, cook ground beef and onion over medium heat until beef is no longer pink, 10-12 minutes, breaking into crumbles; drain. Stir in soups, enchilada sauce, milk and garlic powder. , Place half of the broken taco shells in a 13x9-in. baking dish. Layer with half of the meat mixture and half the cheese. Repeat layers using remaining taco shells, meat mixture and cheese. Bake until heated through, 40-45 minutes. Let stand 5 minutes before serving.