Heat olive oil in a large skillet over medium heat.
Sauté sliced onions and bell peppers for 4 to 5 minutes until softened.
Add thinly sliced beef, season with salt, pepper, garlic powder, and Italian seasoning, then cook until beef is browned.
Remove skillet from heat and let the mixture cool slightly.
Stir in shredded mozzarella and optional provolone or cheddar cheese.
Preheat oven to 400°F (200°C).
Roll out pizza dough on a lightly floured surface into a 12 by 16 inch rectangular shape.
Spread the beef and vegetable filling evenly on one side of the dough, leaving a 1 to 2 inch border.
Carefully roll the dough over the filling, tucking edges in as you go, forming a sealed log.
Pinch the seam and ends of the dough to fully seal the stromboli.
Place the stromboli seam-side down on a parchment-lined baking sheet.
Brush the top with beaten egg to create a golden, shiny crust.
Optionally, make small slits on top to allow steam to escape during baking.
Bake for 20 to 25 minutes until the crust is golden brown and cooked through.
Let the stromboli rest for 5 minutes before slicing and serving warm.
Serve with marinara or pizza sauce for dipping if desired.