In a large mixing bowl, combine the flour, sugar, salt, and instant yeast. Mix well.
Add the warm water and olive oil to the dry ingredients. Stir until a dough forms.
Knead the dough on a floured surface for about 5 minutes until smooth and elastic.
Place the dough in a greased bowl, cover with a kitchen towel, and let it rise in a warm place for about 30 minutes or until doubled in size.
Preheat your oven to 400°F.
Once the dough has risen, roll it out on a floured surface into a rectangle about 1/4 inch thick.
Spread the mozzarella cheese evenly over the dough, leaving a small border around the edges.
Layer the pepperoni, cooked sausage, bell peppers, and olives on top of the cheese. Sprinkle with Italian seasoning.
Starting from one long side, carefully roll the dough into a log shape. Pinch the seams to seal.
Place the rolled stromboli seam-side down on a baking sheet lined with parchment paper.
Beat 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 golden brown.
Allow to cool for a few minutes before slicing. Serve with marinara sauce for dipping.