Spray a large non-stick skillet with cooking spray and heat oven medium-high heat. Add ground beef, onion and garlic and cook, stirring occasionally, for 5 minutes, or until the beef is cooked. Drain excess fat.
Add Taco seasoning, refried beans, salsa and tomato sauce to the meat mixture in the skillet, and mix until combined. Cook, stirring every 30 seconds, for 5 minutes. Add salt and pepper to taste if needed.
Spray a non-stick 9x13 baking dish with cooking spray (or grease with butter).
Layer half of corn tortilla pieces on the bottom of the baking dish.
Spread half of the meat sauce over the tortilla layer.
Sprinkle the meat sauce layer with half of the shredded cheese.
Layer the remaining tortilla pieces on top of the cheese, followed by a layer of remaining meat sauce and remaining shredded cheese.
Put the enchilada casserole in the oven and bake for 30 minutes.
Remove the enchilada casserole from the oven and sprinkle with green onions.