Adjust the oven temperature to 425°F (220°C) and place parchment paper on a baking pan.
Roll out the pizza dough onto a floured board into a large circle or rectangle that is about ¼ inch thick.
Leaving a thin border all the way around, cover one half of the dough with marinara sauce.
Add the olives, bell peppers, mushrooms, pepperoni, and mozzarella cheese on top of the sauce.
Pressing down firmly on the edges to seal, fold the empty half of the dough over the filling. For a decorative seal, crimp the edges using a fork.
After transferring the calzone to the ready-made baking sheet, cut a few tiny slits in the top to let out steam and spray the top with olive oil for a golden crust.
Bake for twenty to twenty-five minutes.