Preheat the oven to 375 degrees F (190 degrees C). Lightly grease a 9x13-inch baking dish.

Bring a large pot of lightly salted water to a boil. Add ziti pasta and cook until tender yet firm to the bite, 8 to 10 minutes; drain and rinse.

Combine cooked ziti, ricotta cheese, mozzarella cheese, 1 ½ cups spaghetti sauce, and beaten egg in a medium bowl. Mix well.

Transfer into the prepared baking dish. Top with remaining spaghetti sauce, then sprinkle with Parmesan cheese.

Bake in the preheated oven for 30 minutes; let stand for 15 minutes before serving.