First, you are to dice your onions, chop the potatoes into 1-inch cubes and mince your garlic. Set your Ninja Foodi on saute, high and let it warm up. Add the oil now too. You can use olive oil or vegetable oil or any oil you prefer. I used Extra Virgin Olive Oil. You will know the oil is hot when it starts to glisten. Add the stew meat, salt, pepper, and Italian seasoning to the Ninja Foodi. You want to brown the meat on all sides. Once the meat is browned, add the beef stock and use a spatula or wooden spoon to clean off the sides of the pot. Next, add the Worchestershire sauce, garlic, onion, carrots, potatoes, and tomato sauce. Place the pressure cooking lid on your Ninja Foodi and be sure the steam vent is closed. Set the Ninja Foodi on pressure cook, high for 35 minutes. When it's done, let it do a natural release for 10 minutes then open the steam valve and finish with a quick release. In a small bowl, combine the cornstarch and water. Stir the mixture until the cornstarch is dissolved. Pour the mixture into the beef stew and stir until the sauce starts to thicken. This is great with a piece of crusty bread too.