Brown ground beef and onion until onion is clear, drain and set aside. Stir in mushroom soup. ranch style beans and rotel tomatoes and cook on medium heat 10 minutes or until hot.
In a 9x13 inch casserole dish, cover the bottom of the dish with torn tortilla's until covered. Spoon a thin layer of the meat mixture over the tortilla's and then a layer of shredded cheese. Repeat layers until mixture is used and follow with cheese and a few torn tortilla's and black olives. Place in 350 degree oven until cheese starts to brown. Serve with Tostido chips, salsa and sour cream. (optional).