1Heat grill. Drizzle taco sauce evenly over pizza crusts. Spoon half of the ground beef in taco sauce onto each pizza; spread evenly. Sprinkle each with 1 cup of the cheese. Arrange tomato slices over cheese on each pizza. Sprinkle evenly with remaining 2 cups cheese.
2When ready to grill, place pizzas on gas grill over medium heat or on charcoal grill 4 to 6 inches from medium coals. Cook 10 to 15 minutes or until crust is crisp and toppings are thoroughly heated. If crust browns too quickly, place sheet of foil between crust and grill rack.
3Sprinkle lettuce over pizzas. Serve with guacamole and sour cream, if desired.