Using a 3 to 4-quart saucepan, sauté the ground beef over medium-high heat. Drain any excess grease.
Add the water and taco seasoning. Stir to combine and continue to cook over medium heat for an additional 5 minutes. Remove from heat and set it aside.
Line a standard baking sheet with paper towels and set it aside.
Preheat the oven to 400°F. Line 2 baking sheets with foil and lightly spray with nonstick spray. Set them aside.
Using a 10 or 12-inch skillet over medium-high heat, add the vegetable oil.
Carefully add the flour tortillas one at a time, cooking for 1½ to 2 minutes per side. Be careful not to burn the tortillas. Carefully transfer the cooked tortillas to the paper towel-lined baking sheet to drain. Repeat the process until all tortillas are cooked.
Place 1 of the cooked tortillas on the prepared baking sheet.
Spread ¼ cup of refried beans over 1 tortilla.
Evenly sprinkle ¼ cup of the seasoned cooked ground beef over the refried beans.
Evenly sprinkle 2 tablespoons of the shredded cheddar cheese over the seasoned ground beef.
Lay a second tortilla on top of the first layer. Spread 2 tablespoons of the red enchilada sauce.
Evenly sprinkle 2 teaspoons of diced tomato on top of the enchilada sauce.
Evenly sprinkle ¼ cup of shredded cheddar cheese over the tomato layer.
Once you have made the double-decker pizzas, bake for 7 to 8 minutes or until the cheese is completely melted.
Remove from the oven and slice as you would a pizza. Since the pizzas are smaller, slice the pizzas into 4 pieces. Top with sour cream, sliced black olives, and thin sliced green onion, if you wish. Serve while hot.