Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper or lightly grease it.

Roll out the pizza dough into a rectangle on a lightly floured surface. Sprinkle mozzarella and Parmesan cheeses evenly over the dough, leaving about 1-inch border around the edges.

Arrange pepperoni slices over the cheese. Sprinkle dried oregano, garlic powder, and red pepper flakes (if using) over the top.

Starting from one edge, carefully roll the dough into a tight log, enclosing the filling inside. Pinch the edges to seal the stromboli.

Place the stromboli seam-side down on the prepared baking sheet. Brush the top with the beaten egg for a golden, shiny finish.

Make a few diagonal slits on top of the stromboli to allow steam to escape while baking.

Bake for 20–25 minutes, or until the stromboli is golden brown and the cheese is melted inside.

Remove from the oven and let cool for a few minutes before slicing. Serve with marinara sauce for dipping.