Preheat your oven to 375°F (190°C) and line a baking sheet with parchment paper.
Roll out the pizza dough on a floured surface into a large rectangle.
Spread the marinara sauce over the dough, leaving a 1-inch border around the edges.
Sprinkle the shredded mozzarella cheese evenly over the sauce.
Layer the bell peppers, mushrooms, and spinach on top of the cheese.
Drizzle the olive oil over the vegetables and sprinkle with Italian seasoning, garlic powder, salt, and black pepper.
Carefully roll up the dough from one long side to the other, sealing the edges as you go.
Place the stromboli seam-side down on the prepared baking sheet.
Bake for 25 minutes or until golden brown and cooked through.
Let cool for a few minutes before slicing and serving.