Bring a large pot of lightly salted water to a boil. Add ziti and cook for 8 to 10 minutes or until al dente; drain and rinse.
In a medium bowl, mix ziti, ricotta cheese, mozzarella cheese, egg and 1 1/2 cups spaghetti sauce.
Preheat oven to 375 degrees F (190 degrees C).
Lightly grease a 9x13 inch baking dish and spoon in ziti mixture. Top with remaining spaghetti sauce, followed by Parmesan cheese.
Bake in preheated oven for 30 minutes; let stand for 15 minutes before serving.