Preheat your oven to 375°F.
Chop ¾ of the mini pepperoni into ¼-inch pieces and set aside.
Combine the flour, garlic salt, onion powder, oregano, baking powder, and grated parmesan cheese in a large mixing bowl.
Add the milk, egg, melted butter, and half the package of chopped pepperoni to the batter and stir to combine. Note that the batter will be runny.
Spray a regular-sized 12-serving muffin tin with cooking spray.
Fill the bottom of the muffin pan ¼ of the way full with batter, then sprinkle 1 tablespoon of shredded cheddar cheese in the middle.
Add more batter on top of the cheese, filling it only about ¾ of the way full.
Add a dollop of pizza sauce on the top, sprinkle with more cheddar, and add mini pepperoni. Then press ingredients down into batter just a bit.
Bake at 375°F for 20 to 22 minutes, depending on how hot your oven runs.
Let the muffins rest in the muffin tin for 5 minutes before removing them.