Set the pot on sauté mode, and allow to heat. Add 1 tablespoon olive oil, and sauté 1 cup finely chopped onion until softened, then add 2 cloves minced garlic and cook for about 30 seconds.
Add 1 pound lean ground beef, and brown. Drain if necessary.
Add 12oz spaghetti (I break it up and put it in the pot in varying directions - a criss cross pattern works well!).
Pour 24 ounces marinara sauce over the top, and then pour 2 1/2 cups water around the sides. Sprinkle over 1 tablespoon Italian Seasoning DO NOT STIR.
Place the lid on the instant pot, and set to seal, and cook on high pressure for 8 minutes.
Do a natural pressure release for 5 minutes, then perform quick release.
Remove the lid, stir the food until well combined.