Bring a large pot of lightly salted water to a boil. Add ziti pasta, and cook until al dente, about 8 minutes; drain.
Brown onion and ground beef over medium heat. Add spaghetti sauce, and simmer 10 minutes.
Spray a 9x13 inch baking dish. Layer as follows: 1/2 of the ziti, Provolone cheese, sour cream, 1/2 sauce mixture, remaining ziti, mozzarella cheese and remaining sauce mixture. Top with grated parmesan cheese.