Preheat oven to 400 degrees.
Place ground beef and onion in a nonstick pan and cook over medium heat, breaking apart with a wooden spoon until no longer pink. Add garlic.
Measure out 1 1/2 teaspoons taco seasoning and set aside. Add remaining taco seasoning and 1/4 cup water to ground beef. Stir well and cook until evenly mixed and thickened. Remove from heat.
Spray both sides of tortillas with cooking spray. Place on baking sheets and bake 3 minutes. Flip over and bake another 3 minutes.
Mix the 1 1/2 teaspoons taco seasoning into the refried beans. Mix in 1/3 cup shredded cheese.
Divide ground beef mixture on 3 of the tortillas and spread evenly. Sprinkle about 2 tablespoons of cheese on top of each one and top with a second tortilla. Spread 1/3 of refried bean mixture on top of each tortilla that was just stacked.
Top with remaining tortillas and sprinkle about 1/4 cup shredded cheese on top of each pizza.
Place in oven and bake until cheese is melted, about 6-8 minutes.
Place desired toppings on top and cut into wedges to serve.