Preheat the oven as directed on your pizza crust recipe or package. If using an uncooked crust, we like to bake it halfway before topping it.
Add 1 tablespoon of the olive oil to a large skillet over medium-high heat.
Slice the sausage into ¼" rounds and add them to the skillet. Sauté until lightly browned on both sides.
Remove the sausage from the pan, and add the remaining tablespoon of olive oil along with the onions.
Sauté the onions for about 5 minutes or until nicely browned and caramelized. Be sure to stir them frequently.
While the onions are cooking, you can start preparing the pizza.
Spread the ricotta in an even layer all over the crust.
Sprinkle the ricotta with the pepper and then drizzle it with two tablespoons of olive oil.
Sprinkle on one cup of the mozzarella followed by ¼ cup of the Parmesan cheese.
When the onions are done and cool enough to handle, distribute them evenly on the pizza followed by the sausage.
Add the remaining ½ cup of mozzarella cheese and ¼ cup Parmesan cheese to the top.
Place the pizza in the oven and bake until the cheese is melted and the edges are lightly browned.
When the pizza comes out of the oven, sprinkle the arugula all over the top, slice, and serve immediately.