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 12 inches by 18 inches).
In a mixing bowl, combine the mozzarella cheese, pepperoni, cooked sausage, bell pepper, onion, Italian seasoning, salt, and pepper. Mix well.
Spread the filling mixture evenly over the rolled-out dough, leaving a 1-inch border around the edges.
Starting from one end, carefully roll the dough tightly into a log shape, making sure to keep the filling inside. Pinch the edges to seal.
Transfer the rolled Stromboli to the prepared baking sheet. If using, whisk the egg and brush it over the top of the Stromboli for a golden finish.
Bake in the preheated oven for 20-25 minutes, or until the crust is golden brown and cooked through.
Remove from the oven and let it cool for a few minutes before slicing. Serve warm.