Preheat oven to 375°F. Coat 16 cups of 2 muffin pans with the cooking spray. Cut the mozzarella into 16 small cubes.
Pat the peppers dry and finely chop. Add to a medium bowl, along with ¼ cup pizza sauce. Stir to combine. Separate the biscuits and cut each in half to get 16 pieces.
Roll and stretch each piece of dough until very thin. Place 4 slices pepperoni in center of dough. Spoon 1 tsp of sauce mixture onto pepperoni. Place 1 cube of cheese on sauce. Pinch dough tightly to close around filling. Place in 1 cup of muffin pan, seam-side down. Repeat with remaining biscuits and filling.
Lightly coat tops with cooking spray. Sprinkle with the garlic powder and Parmesan. Bake 15–20 min., until golden brown. Serve with remaining ½ cup pizza sauce.