Brown the hamburger with the chopped onion, drain grease. Add the tomato sauce, chili powder, garlic salt, salt, and pepper. Let the meat mixture simmer for 5-10 minutes.
Combine the soup with the milk. Grease a 9-inch by 13-inch pan and preheat the oven to 350 degrees. Place six of the tortillas in the pan then spread the meat mixture on the tortillas. Add another layer of the tortillas. Next, pour the soup mixture on top and sprinkle with the grated cheese. Cover with foil. Bake at 350 degrees for 30-40 minutes until heated thoroughly.