Prepare the Filling: In a skillet over medium heat, heat olive oil. Sauté onions and bell peppers for 3-4 minutes until softened. Add garlic powder, salt, black pepper, and Italian seasoning. Stir in the sliced ribeye or roast beef and cook for another 2-3 minutes until heated through. Remove from heat and let cool slightly.

Assemble the Stromboli: Preheat oven to 400°F (200°C). Lightly flour a work surface and roll out pizza dough into a rectangle (about 12×16 inches). Evenly spread the steak and veggie mixture over the dough, leaving a 1-inch border. Sprinkle shredded mozzarella and provolone cheese on top.

Roll and Seal: Carefully roll up the dough from the long side, tucking in the edges as you go. Place seam-side down on a parchment-lined baking sheet.

Bake: Brush the top with melted butter and sprinkle with garlic powder, oregano, red pepper flakes (if using), and Parmesan cheese. Bake for 18-22 minutes or until golden brown and crispy.

Serve: Let cool for 5 minutes before slicing. Serve warm with marinara sauce or cheese sauce for dipping.