Separate biscuits and place on a work surface. Roll biscuits to double their original diameter using a rolling pin. Sprinkle garlic salt over each biscuit and top with 2 pieces pepperoni. Generously sprinkle mozzarella cheese over pepperoni layer, reserving about 2 tablespoons cheese. Fold the edges of each roll over the toppings, pinching the edges together to seal shut. Arrange biscuits on a baking sheet. Sprinkle reserved mozzarella cheese over each biscuit.
Bake in the preheated oven until cheese is melted and biscuits are lightly browned, about 12 minutes.
