Heat the oven to 375°F and grease a 9-by-13-inch dish. Boil the ziti 2 minutes short of done and drain.
Brown the beef and onion in a large skillet. Drain, add garlic for 30 seconds, then stir in crushed tomatoes, tomato sauce, Italian seasoning, 3/4 teaspoon salt and pepper and simmer 8 minutes.
Mix the ricotta, egg, remaining salt, 1 cup mozzarella and Parmesan.
Toss the ziti with the sauce. Spread half in the dish, spoon on the ricotta mixture, add the remaining pasta and top with the remaining mozzarella.
Cover and bake 25 minutes. Uncover and bake 12 to 15 minutes more. Rest 15 minutes before serving.