Heat oil in a large skillet over medium heat for 1-2 minutes until shimmering.

Sauté veggies by adding sliced onions and bell peppers, cooking for 4-5 minutes until softened.

Add thinly sliced beef to the vegetable mixture and season with salt, pepper, garlic powder, and Italian seasoning, cooking until browned for 4-5 more minutes.

Remove from heat and cool slightly.

Mix in shredded mozzarella and optional provolone or cheddar until evenly distributed.

Preheat oven to 400°F (200°C).

Roll out dough on a floured surface into a 12 by 16 inch rectangle.

Spread filling evenly over one half of the dough, leaving a 1-2 inch border.

Roll the dough over the filling, tucking in the edges to form a sealed log.

Pinch the seam and ends of the dough to seal tightly.

Place the stromboli seam-side down on a parchment-lined baking sheet.

Brush the top with beaten egg.

Make slits on top if desired for steam to escape.

Bake for 20-25 minutes until the crust is golden brown.

Let rest for about 5 minutes before slicing.

Serve warm with marinara or pizza sauce for dipping.