Preheat the oven to 350 degrees F (175 degrees C). Spray an 8-quart glass baking dish with cooking spray.
Combine beef, sausage, garlic, dried onion, and garlic salt in a large skillet over medium heat. Cook and stir until meat is almost browned, about 5 minutes. Add mushrooms and olives; cook until mushrooms have browned and olives are heated through, about 5 minutes. Remove from heat.
Layer 6 tortillas in the bottom and up the sides of the baking dish. Spread 1/2 to 3/4 of the pizza sauce over the tortillas. Sprinkle 1 cup of cheese on top. Spoon some of the meat mixture over the cheese; cover with another 1/2 cup of cheese. Continue layering remaining tortillas, sauce, meat, and cheese.
Bake in the preheated oven until hot and bubbly, about 20 minutes.