Preheat oven to 400 degrees. Coat a 9-inch baking dish with nonstick spray. In a small bowl, whisk together melted butter and garlic salt.
Form each biscuit half into a circle and flatten into a disk. Top with one piece of pepperoni and 1/2-ounce piece of mozzarella cheese.
Fold the sides of the biscuit up and over the pepperoni and cheese until it is completely covered. Shape into a ball and place in the prepared pan. Repeat with remaining biscuit halves, 15 pepperoni pieces, and mozzarella cheese pieces.
When all the pizza bites have been formed and placed in the baking dish, arrange the remaining pepperoni (about 24 pieces) between the biscuits.
Brush with garlic butter, top with the shredded mozzarella cheese, and garnish with parsley if desired.