Heat the oven to 375°F. Cook the ziti in salted water until just shy of tender, then drain.

Brown the sausage and onion in a large skillet. Stir in the garlic for 30 seconds, then add the marinara and Italian seasoning.

Mix the pasta with half the sauce. Layer it in a greased baking dish with ricotta, mozzarella, and the remaining sauce.

Sprinkle Parmesan and the rest of the mozzarella over the top. Cover with foil and bake for 20 minutes, then uncover and bake 10 minutes more.