Preheat your oven to 400°F (200°C).
Roll out the pizza dough on a floured surface into a rectangle.
Spread marinara sauce evenly over the dough, leaving a border.
Layer mozzarella cheese over the sauce.
Add pepperoni, spinach, and bell pepper on top of the cheese.
Sprinkle Italian seasoning evenly over the toppings.
Carefully roll the dough from one end to the other to form a log.
Pinch the edges to seal the stromboli securely.
Place the stromboli seam-side down on a baking sheet lined with parchment paper.
Brush the top with beaten egg for a golden finish.
Bake for 25-30 minutes or until golden brown.