Preheat the oven to 500℉. Place a 12-inch cast iron skillet in the oven to preheat.
In another skillet set over medium heat, brown the sausage until cooked through, breaking it apart as it cooks, approx. 5-7 minutes. Drain the sausage on a paper towel-lined plate. Set aside.
Remove the preheated skillet from the oven. Lightly brush the inside of the skillet with oil. Shape the pizza dough to fit the skillet, being careful not to burn yourself on the hot skillet.
Spread 3-4 tablespoons of sauce over the dough. Top with one cup of cheese, half of the sausage, half of the onion, and another ½ cup of cheese. Bake for 12-15 minutes until browned around the edges and cheese is melted and bubbly.