Heat the oven to 375°F (190°C). Lightly grease a 9×13-inch baking dish.
Bring a large pot of lightly salted water to a boil. Cook the ziti for 8–10 minutes, until al dente. Drain and rinse thoroughly.
Combine the cooked ziti, ricotta, mozzarella, beaten egg, and 1½ cups (approximately 355 mL) spaghetti sauce in a large mixing bowl.
Transfer the mixture to the prepared dish. Spread the remaining sauce over the surface and sprinkle with Parmesan.
Bake for 30 minutes, until the cheese is melted, the edges are visibly hot, and the center reaches 165°F (74°C). Continue baking if needed to reach that temperature. Rest for 15 minutes before dividing into eight servings.