Preheat an oven to 400ºF and place 8 tostadas on a large baking sheet (or two baking sheets). Set aside.
Brown the ground beef in a large skillet over medium-high heat. Once cooked, add the taco seasoning, refried beans, and broth. Continue cooking until everything is evenly mixed and no excess liquid remains, about 3-4 minutes.
Top the 8 tostadas with the beef mixture, about 4-5 ounces each. Place the remaining 8 tostadas on top of the beef, sealing the pizzas.
Add 1 tablespoon of taco sauce on top of each pizza, spreading it to the edges to fully coat the top. Sprinkle 1/2 an ounce of shredded cheese on top of the sauce.
Bake for 8-10 minutes or until the cheese is fully melted.
Top with pico de gallo or diced tomatoes, slice into quarters, and serve!