Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper.
On a floured surface, roll out the pizza dough into a rectangle (about 12x15 inches).
Spread the shredded mozzarella cheese evenly over the dough, leaving a border around the edges.
Layer the pepperoni, bell peppers, and mushrooms evenly on top of the cheese. Sprinkle the grated Parmesan and Italian seasoning over the filling, and season with salt and pepper.
Carefully roll the dough from one long edge to the other, making sure to keep the fillings tucked inside. Pinch the edges to seal the dough well.
Place the rolled Stromboli seam-side down on the prepared baking sheet.
Beat the egg in a small bowl and brush it over the top of the Stromboli for a golden finish. Optionally, sprinkle a little Italian seasoning on top.
Cut a few slits on the top of the Stromboli to allow steam to escape.
Bake in the preheated oven for 20-25 minutes, or until golden brown.
Once baked, remove from the oven and let it rest for a few minutes before slicing.