Preheat oven to 350F, and lightly grease a 9x13 glass dish and set aside for later.

In a large saucepan with high sides, add ground beef and onions and cook over medium heat until no pink remains. Start to boil a pot of water for the pasta.

Drain out most of the juices, then add the Italian seasoning, garlic, sea salt and ground pepper and cook for 1 minute.

Add the tomato sauce to the pan and cook while stirring occasionally for about 5 minutes, then set aside.

Cook rigatoni until al dente and reserve ½ cup of the pasta water once complete. Pour the pasta water into the saucepan and stir.

Then add the pasta in, and mix until well combined, then pour into the casserole dish.

Cover with foil and bake at 350F for 20 minutes or until heated thoroughly (note: it is helpful to grease the inside of the foil, so the cheese does not stick).

Uncover and layer with mozzarella cheese and bake uncovered for 5-10 minutes, or until cheese has started to brown.