Brown ground beef in a medium skillet. Add taco seasoning and 1/2 cup water; simmer 5 minutes, stirring occasionally.
Heat refried beans in a small saucepan over medium-low heat.
Spread beans on tostada shells (1-2 Tablespoons per shell).
Spoon meat on top of beans (2-3 Tablespoons per shell).
Top with lettuce, pico de gallo, guacamole, queso fresco, cilantro lime sauce, japeños, and any of your favorite toppings.