Preheat the oven to 350 degrees F.
Cook ziti noodles according to directions on the box until the pasta is al dente, a little firm. You will also be baking this so do not cook pasta al dente. When it is done cooking, drain, return to the pan and set aside. You can toss with a little olive oil to prevent it from sticking together, if desired.
While the pasta is cooking, heat olive oil in a large skillet on medium-high heat. When the oil is shimmering hot add the sausage and cook until it’s brown and crispy. Add the onion to the skillet when the sausage is almost cooked through. Continue to cook over medium-high heat until the onion is soft and translucent.
Add the garlic and Italian seasoning, stir to combine. Season with salt and pepper, if desired. Cook for 1 minute, then add the marinara sauce and stir well. Bring to a simmer.
In a mixing bowl combine the ricotta and Italian cheese.
Add 1 c. of red sauce into the prepared ziti pasta, stir to combine.
Pour half of the ziti into a 9x13’’ baking dish the deeper the better. Add half of the ricotta cheese mixture on top of the ziti in small dollops. Then spoon half of the red sauce over the ricotta. Repeat these layers, pasta, ricotta mixture and sauce. Top with Mozzarella cheese.
Cover the baking dish with foil. Tent the foil so it’s not touching the cheese.
Place the baking dish in a preheated oven for 20 minutes.
After baking time is done, remove foil from the dish. Turn the oven to broil and return the casserole to the oven.
Broil for 3-5 minutes or just until the cheese is lightly browned.
Remove from the oven, top with chopped parsley if desired and serve.