Cut tortillas into wedges. Set aside. Put the beef and onions in a skillet over medium heat. Break up meat while frying. Fry til meat is cooked. Drain off fat, set aside
Mix the chili powder, salt, pepper, ground cumin, black olives, tomato sauce, water and cornstarch well in a bowl. Add meat mixture, tortilla wedges and cheese. Mix thoroughly. Pour into 9 x 13 inch baking dish and bake uncovered in oven at 350 for 30 minutes.