In a large saucepan, stir and cook ground beef and onion over medium heat until browned and onions have softened. Drain any juices released.
Add the Italian seasoning, garlic, salt and pepper and cook 1 minute.
Add the pasta sauce and cook, stirring occasionally, over medium heat, for 5 minutes. Set aside.
Meanwhile, bring a large pot of salted water to a rolling boil over high heat. Add rigatoni, reduce heat to medium-high, and cook just until al dente (it will continue to cook slightly in the oven).
Reserve 1/2 cup pasta water and drain pasta. Stir reserved pasta water into meat sauce.
Combine pasta and pasta sauce in saucepan. Pour into a lightly greased 9x13" or similar baking dish.
Cover with a lightly greased piece of foil and bake at 350 degrees F for 20 minutes or until heated through.
**Optionally, cover and refrigerate up to 2 days. Bake at 350 degrees F until heated through, about 30-40 minutes.
Uncover and sprinkle with cheese. Bake an additional 10 minutes, until cheese has started to brown.