Preheat the oven to 375°F. Bring a large pot of water to a boil and cook the ziti according to package directions until just al dente. Drain and set aside.

Heat the olive oil in a large skillet over medium heat. Add the Italian sausage and cook, breaking it up with a spoon, until browned and cooked through.

Stir the marinara sauce into the skillet with the sausage and let it simmer for 2 minutes to combine the flavors.

Add the drained ziti to the skillet and toss until the pasta is evenly coated with the sausage and sauce mixture.

Transfer half the pasta mixture to a baking dish. Sprinkle with half the mozzarella cheese. Add the remaining pasta mixture and top with the rest of the mozzarella.

Bake uncovered for 20 to 25 minutes until the cheese is melted and the edges are bubbly. Let it rest for 5 minutes before serving.