Preheat oven to 350 degrees F / 175 degrees C.
On silicone mat or parchment-lined baking sheet, divide 1 cup mozzarella cheese into three circles.
1 cup mozzarella cheese
Bake for 12 to 15 minutes, until bottoms are golden.
In mixing bowl, combine 6 ounces crabmeat, 2 tablespoons mayonnaise, 2 tablespoons lemon zest, 2 tablespoons lemon juice, and half of the scallions.
6 ounces crabmeat, 2 tablespoons mayonnaise, 2 tablespoons lemon zest, 2 tablespoons lemon juice, 3 scallions
Divide 6 tablespoons guacamole evenly among tostadas, about 2 tablespoons per tostada.
6 tablespoons guacamole
Garnish with 1 tablespoon chopped cilantro and remaining scallions.
1 tablespoon chopped cilantro
Serve and enjoy.