Preheat oven to 350. Prepare a 13 x 9 baking dish with cooking spray.
Cook beef in onion until cooked through. Drain grease and add the onion and garlic and saute 5 minutes longer.
Stir in the next 5 ingredients then season with the seasonings, simmer 10 minutes.
Spread 1 cup of mixture on bottom in pan and top with 2 tortillas. Spread 1 cup of meat mixture and some cheese. Layer another 2 tortillas, 1 cup meat mixture and cheese. Place third layer, ending with cheese.
Bake in heated oven until heated through and cheese is melted. Cool slightly before serving. Serve with sour cream and avocado slices!