Preheat oven to 375°F. Grease baking dish with olive oil.
Cook ziti pasta until al dente. Drain and set aside.
Heat oil in large skillet over medium heat.
Add diced onion and cook until softened.
Add minced garlic and cook one minute more.
Add Italian sausage and cook until browned completely.
Stir in marinara sauce and simmer five minutes.
Mix ricotta, egg, and basil in bowl.
Layer half pasta in prepared baking dish.
Spread ricotta mixture over pasta evenly.
Top with half mozzarella and meat sauce.
Add remaining pasta and sauce on top.
Sprinkle remaining mozzarella and Parmesan cheese.
Cover with foil and bake 30 minutes.
Remove foil and bake 15 minutes more.
Let rest 10 minutes before serving.