Preheat your oven to 400°F (200°C).
Dust a clean surface with flour and roll out the pizza dough into a rectangle.
Spread a thin layer of marinara sauce over the dough, leaving a border around the edges.
Sprinkle mozzarella cheese evenly over the sauce.
Add pepperoni slices, bell peppers, and onions on top of the cheese.
Sprinkle Italian seasoning over the fillings for added flavor.
Carefully roll the dough from one long side to the other, tightly enclosing the filling.
Pinch the ends to seal and place the stromboli seam-side down on a baking sheet.
Brush the top of the dough with beaten egg and a little olive oil.
Bake in the preheated oven for 25-30 minutes until golden brown.