Preheat an oven to 180 degrees C. Grease a 20x30cm baking dish.
Fill a large saucepan with lightly salted water and bring to a rolling boil over high heat. Once the water is boiling stir in the ziti and return to a boil. Cook the pasta uncovered, stirring occasionally until the pasta has cooked through but is still firm to the bite; about 8 minutes. Drain well in a colander set in the sink.
While pasta is cooking heat a large frypan over medium heat. Add the sausage and cook stirring until brown; about 10 minutes. Drain sausage and set aside.
Stir together the ricotta, egg, onion, garlic and oregano in a large bowl until well combined. Stir in the drained pasta, the drained sausage, salt, pepper and the spaghetti sauce; mix well.
In the prepared baking dish cover the bottom with 1/3 the spaghetti sauce. Layer 1/2 of the pasta mixture, 1/3 of the spaghetti sauce and 1/2 of the grated cheese. Then layer the remaining 1/2 of the pasta, 1/3 of the sauce and 1/2 of the cheese. Sprinkle with basil. Cover the dish tightly with aluminium foil.
Bake in the preheated oven until heated through; about 20 minutes. Uncover; return to the oven and bake until cheese is melted; 5 to 10 more minutes.