Preheat the oven to 350 degrees. In a frying pan cook ground beef and onion in oil until the beef is no longer pink. Drain well. Add refried beans and taco seasoning, stir well and heat through.
In a medium bowl mix cream of mushroom soup and sour cream. Spread half of this mixture in the bottom of a 9×13-inch baking dish.
Arrange a layer of 3 tortillas over a sour cream-soup mixture slightly overlapping them. Top tortillas with a layer of the beef mixture and sprinkle with half of the shredded cheese.
Continue to layer all of the remaining ingredients in the same order and top with the rest of the cheese.
Bake for 20 minutes or until cheese is melted and enjoy!