Fill a large pasta or stock pot with water; salt generously. Bring to a full boil. When the water comes to a rapid boil, add the ziti; stir and bring back to a full boil. Cook uncovered until the pasta is al dente, usually about 8 - 10 minutes; stirring occasionally. Drain, but do not rinse.
While the pasta is cooking, brown and break up the sausage in a large skillet. Add chopped onion and garlic, cook until onions are tender and translucent. Drain fat and set aside.
In a large bowl, whisk together the ricotta, egg, and oregano. Stir in the sausage mixture, 1 jar of the spaghetti sauce, and the drained pasta. Season with salt and pepper.
In the greased baking dish, pour 1/3 of the second jar of spaghetti sauce and spread to coat bottom of dish. Layer 1/2 of the ziti mixture on top of the spaghetti sauce. Top the pasta with 1/2 of the sauce remaining in the jar and 1/2 of the shredded Italian cheese. Repeat layers with remaining pasta and spaghetti sauce; top with remaining shredded cheese. Sprinkle the top of the casserole with dried basil.
Cover tightly with lightly greased aluminum foil. Place on sheet pan and bake about 20 minutes; until heated through. Uncover and bake an additional 5 to 10 minutes until the cheese is melted and golden brown.