Preheat oven to 350 degrees. Spray a 9x11" baking pan with non-stick cooking spray.
In a large skillet, brown ground beef over medium-high heat. Cook until meat is no longer pink and fully cooked (about 6-9 minutes).
In a large bowl, toss together cooked ground beef, half of the enchilada sauce, and half of the cheese.
Place 4 of the tortillas on the bottom of the prepared baking dish, ripping them if necessary to cover the bottom of the pan.
Top the tortillas with half of the beef mixture, half of the beans and drizzle with 1/4 cup of enchilada sauce.
Repeat all layers one more time.
Top with remaining shredded cheese and cover pan with foil. Bake for 30 minutes or until casserole is cooked through.
If desired, top with tomatoes and avocado.