1. Preheat oven to 350°F. Line a large baking sheet with foil and a plate with paper towels. In a heavy medium skillet over medium heat, season ground beef with salt and pepper and cook, stirring to break up large chunks, until beef is no longer pink, about 5 minutes. Remove from heat. Using a slotted spoon, transfer meat to lined plate to drain.
2. Lay pizza crusts on prepared baking sheet. On each crust, using the back of a spoon, evenly spread 1/3 of refried beans, leaving a 1/2-inch border around edges. Divide ground beef, salsa and cheese among crusts, spreading evenly over refried beans.
3. Bake pizzas until cheese is bubbling, about 15 minutes. Just before serving, sprinkle pizzas evenly with lettuce and tomato, slice and serve with extra salsa, if desired.