Preheat your oven to 350°F (175°C). In a large skillet, cook the ground beef and chopped onion over medium heat until the beef is no longer pink. Drain any excess fat. Add the taco seasoning and refried beans to the skillet, mixing well. Heat the mixture through.

In a separate bowl, combine the cream of mushroom soup and sour cream, creating a creamy blend. Spread half of the soup mixture evenly on the bottom of a baking dish. Place a layer of 3 flour tortillas on top of the soup mixture, tearing and overlapping them to fit.

Spread a layer of the ground beef mixture on top of the tortillas, and then sprinkle a cup of shredded Mexican blend cheese over the beef. Repeat these layers once more, ending with a final layer of cheese on top.

Bake the casserole in the preheated oven for approximately 20 minutes or until the cheese is beautifully melted and bubbly. Once done, remove from the oven and let it rest for a few minutes. Serve this delectable dish to your loved ones and relish the flavors!