Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
On a lightly floured surface, roll out the pizza dough into a rectangle approximately 12x16 inches.
Sprinkle the shredded mozzarella cheese evenly over the dough, leaving a small border around the edges.
Layer the pepperoni, bell peppers, and crumbled sausage (if using) on top of the cheese.
Sprinkle the grated Parmesan cheese, Italian seasoning, and garlic powder evenly over the fillings.
Starting from one long side, carefully roll the dough up tightly into a log shape. Pinch the seams to seal.
Place the rolled Stromboli seam-side down on the prepared baking sheet.
In a small bowl, beat the egg and brush it evenly over the top of the Stromboli for a golden finish.
Bake in the preheated oven for 25 minutes, or until golden brown and cooked through.
Remove from the oven, let it cool for a few minutes, then slice into pieces and serve with marinara sauce for dipping.