Preheat the oven to 500 degrees. Oil a 10-inch cast iron skillet. Roll out or stretch dough to fit into skillet, pressing it with oiled fingers until it comes 2 inches up the sides and is an even thickness on bottom. Let dough rise in a warm place for 10 minutes.
In a skillet set over moderate heat cook the sausage, stirring, until it is no longer pink. Transfer to a plate. Add 2 tablespoons oil to the skillet and heat it until hot. Add the peppers, onion, salt and pepper and cook the mixture, stirring occasionally, until vegetables are softened, about 5 minutes. Add the garlic and cook, stirring, 1 minute. Return the sausage to the pan, add the Marinara sauce and oregano and simmer the mixture, stirring occasionally, for 10 minutes more.
Sprinkle dough with half of mozzarella and top with sausage mixture and remaining mozzarella. Sprinkle with Parmesan and drizzle with remaining oil. Bake in lower third of an electric oven or on floor of a gas oven for 15 minutes. Reduce oven temperature to 400 degrees. and bake 10 minutes more, or until crust is golden. Sprinkle with basil.