Cook hamburger, onion and green peppers together until done. Drain, Add taco seasoning, mushrooms and tomatoes. Mix this with refried beans and cottage cheese. Grease 11x15-inch pan. Put in a layer of tortilla shells. Layer hamburger mixture, shredded cheese and just keep puttin in layers. Cook at 350 degrees, 30-35 minutes. Let set 10 minutes before cutting.