Brown hamburger meat and onions. Once browned, add taco seasoning according to pkg directions and let simmer for about 5 mins. Then add garlic powder, beans and green chiles.
In a 13X9 casserole dish, layer tortillas, meat mixture and then cheese and repeat to top of dish..ending with cheese. Bake at 350 for 30 mins or until cheese is browned. Serve with sour cream and black olives if you wish.