Preheat oven to 375°F. Line a baking sheet with parchment paper and set aside.
Add the pepperoni to a food process and pulse until you get small chunks.
Spread flour on dry surface and roll out dough into a 10 x 15 inch rectangle. Brush the dough with beaten egg. Spread pepperoni, mozzarella and Parmesan cheese evenly over the dough.
Roll up dough like a jelly roll and pinch seam to seal it. Place the bread, seam side down, on prepared baking sheet.
In a microwavable-safe bowl, melt the butter for about 30 seconds and mix in the Italian seasoning and garlic powder. Brush the bread with the melted butter.
Bake in oven for 25-30 minutes, or until golden. Remove and let sit for 3-5 minutes before serving.
Notes
Place frozen dough in the fridge the night before so it is thawed when ready to use.
Use a log of pepperoni if you can find it or thickly cut pepperoni so you get get big chunks when you throw in food processor.
Use freshly grated Parmesan. Never buy pre-shredded Parmesan cheese as it contains wood pulp. Blocks of Parmesan cheese are also cheaper.
If your rolled log is too long for the baking sheet, just shape it so it fits. It doesn't matter how it looks as you're going to slice it.
Don't be worried if some cheese oozes out as that's normal.