Preheat the oven to 350 degrees F (175 degrees C). Grease a 9x13-inch baking dish.
Bring a large pot of lightly salted water to a rolling boil over high heat. Stir in ziti and return to a boil. Cook pasta uncovered, stirring occasionally, until cooked through but still firm to the bite, about 8 minutes. Drain well.
While pasta is cooking, heat a large skillet over medium heat. Add sausage; cook and stir until brown, about 10 minutes. Drain sausage and set aside.
Stir together ricotta, onion, egg, garlic, and oregano in a large bowl until well combined. Stir in pasta, sausage, salt, pepper, and the half jar of spaghetti sauce; mix well.
Cover the bottom of the prepared baking dish with 1/3 of the full jar spaghetti sauce. Layer with 1/2 of the pasta mixture, 1/2 of the remaining spaghetti sauce, and 1/2 of the shredded cheese. Repeat layers once more using remaining pasta, sauce, and cheese. Sprinkle basil over top and cover the dish tightly with aluminum 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.
