In a large bowl, whisk together the flour, baking powder, garlic powder, oregano and pepper. Whisk in the lightly beaten egg and milk.
Add the mozzarella and pepperoni; combine well. Let stand for 5-10 minutes.
Preheat the oven to 375 degrees F. Grease a mini muffin pan with canola oil or cooking spray. Divide the batter evenly between the muffin cups.
Bake until puffed and golden, about 25-30 minutes.
Remove from the oven and allow to cool for about 5 minutes. Use a knife to loosen the pepperoni muffins from the sides of the pan, if necessary.
Serve the puffs with ketchup, hot sauce or any kind of pizza sauce you like.