Preheat your oven to 400°F (200°C).
On a floured surface, roll out the pizza dough into a rectangle.
Spread marinara sauce evenly over the dough, leaving a border around the edges.
Sprinkle mozzarella cheese over the sauce.
Add pepperoni slices, spinach, and bell peppers evenly on top of the cheese.
Sprinkle Italian seasoning over the fillings.
Carefully roll the dough from one end to the other, creating a log shape.
Pinch the edges to seal and place the stromboli seam-side down on a baking sheet.
Brush the top with beaten egg and make a few slits on top for steam to escape.
Bake for 30-35 minutes until golden brown. Let it cool for a few minutes before slicing.