Preheat the oven to 400 degrees F. Heat a skillet over medium-high heat with 2 tablespoons olive oil. Cook the sausage rounds until they turn brown on each side, 8 to 10 minutes.
Grease the inside of a 12-inch cast-iron skillet with the butter. Place the pizza dough in the center and spread evenly towards the bottom edge and 1 1/2 inches up the sides.
The order of layers is very important to achieving a crisp bottom crust. Begin with the sausage. Evenly lay the sausage on the dough, followed by the mozzarella and marinara. Sprinkle the garlic and oregano on top. Finish with the Parmesan and drizzle with the remaining 2 tablespoons olive oil.
Place the skillet pizza on the bottom rack of the oven and cook until the edge of the crust is golden brown and crusty, 30 to 35 minutes. Remove and let rest for 5 minutes before serving.