Heat waffle iron and grease with cooking spray. Using your hands or a rolling pin, roll out biscuits into flat patties. Top half of biscuits with 1/2 cup of mozzarella and 1 tablespoon of pizza sauce, then sprinkle with pepperoni. Top each with a second biscuit and seal edges. Working with one at a time, cook waffles until golden and cooked through, 3 to 5 minutes. Sprinkle with Parmesan and cut into wedges.