Heat oven to 425°F. Lightly oil four muffin cups; dust with a pinch of cornmeal.
Stir melted butter with garlic powder and oregano; set aside for brushing.
Divide dough into 4 equal pieces. Press each into a 4–5 inch round or square.
Press dough into the prepared muffin cups to form deep wells with overhanging corners.
Spoon a little pizza sauce into each cup. Add mozzarella and chopped pepperoni.
Fold the dough corners over the filling and pinch gently to seal the tops.
Brush tops with the garlic-butter mixture.
Bake 13–16 minutes, until puffed, deeply golden, and the cheese is bubbling.
Brush lightly with any remaining butter. Add a small spoon of warm sauce on top, then sprinkle Parmesan and red pepper flakes.
Let rest 3 minutes. Loosen edges and lift out. Finish with parsley and serve hot.