Preheat oven at 325°F. Brown onion and ground beef in large skillet. Add tomato paste, enchilada sauce and water. Then add pinto beans.
Place a layer of this mixture in a greased 2 quart baking dish. Cover with 3 tortillas and a layer of sliced cheese. Add another layer of mixture, 3 tortillas and sliced cheese. Continue alternating layers. Top with cheese.