Other optional toppings: Sour cream, cilantro, avocado, guacamole, sliced jalapenos
Preheat oven to 375 degrees F. Line 2 large baking sheets with foil and spray with nonstick cooking spray. Divide the 8 flour tortillas onto baking sheets and bake for 5 minutes. Using tongs or a spatula, flip each tortilla over and bake 5 minutes more until crispy. Remove from the oven and set aside. *Watch closely - they will burn quickly.
Meanwhile, heat a large skillet over medium heat. Add ground beef and cook, breaking up into very small pieces with a spatula, until no longer pink. Add taco seasoning and water and bring to a simmer, then simmer for 5-10 minutes.
In a small saucepan, heat refried beans with 1-2 tablespoons of milk (optional, but helps to make the beans nice and creamy).
Prepare the Mexican pizzas on the foil lined baking sheets. Set out one tortilla and spread a thin layer of the beans evenly on top. Add about ⅓ of the meat mixture, spreading evenly, then top with a second tortilla. Spread a few tablespoons of enchilada sauce on top, then add diced tomatoes, shredded cheese, sliced olives and green onions. Repeat for the remaining 3 pizzas.
Bake the pizzas in the preheated oven for about 5 minutes or until cheese is melted and bubbly.
Feel free to customize the toppings or the types of cheese.