Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper.
Roll out the pizza dough on a lightly floured surface to form a rectangle.
Sprinkle garlic powder and Italian seasoning evenly over the dough.
Spread mozzarella and Parmesan cheeses over the dough, leaving a 1-inch border.
Add a layer of pepperoni slices evenly over the cheese.
Starting from one long side, carefully roll up the dough like a jelly roll and pinch the edges to seal.
Transfer the Stromboli to the prepared baking sheet, seam-side down.
Brush the top with the beaten egg for a golden finish.
Bake for 20–25 minutes, or until golden brown and cooked through.
Let cool slightly, slice, and serve with marinara sauce if desired.