Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper.
On a lightly floured surface, roll out the pizza dough into a rectangle that is about 12x15 inches.
Sprinkle the shredded mozzarella cheese evenly over the dough, leaving a small border around the edges. Layer the pepperoni slices and olives on top of the cheese. Sprinkle the Parmesan cheese, Italian seasoning, garlic powder, and red pepper flakes over the toppings.
Starting from one of the long edges, carefully roll the dough into a tight log, making sure the filling stays inside. Pinch the seams and ends to seal it well.
Place the Stromboli seam-side down on the prepared baking sheet. Brush the top of the dough with the beaten egg for a golden finish.
Using a sharp knife, make 3-4 slits on top of the Stromboli to allow steam to escape during baking.
Transfer to the preheated oven and bake for 25-30 minutes, or until golden brown and fully cooked.
Once baked, remove from the oven and let it cool for about 5-10 minutes. Slice into pieces and serve warm with marinara sauce on the side for dipping.