Add the ground beef, minced onion, and garlic powder to the Instant Pot insert. Set on Saute mode and brown the ground beef in the insert. Once browned, stir in the marinara sauce.
Break the noodles in half or thirds and mix into the sauce and then pour the beef/chicken stock/water over the top. Give it a gentle stir and then press all the noodles into the liquid.
Close the lid, set to sealing.
Set on Manual, High Pressure and cook for 6 minutes.
Let naturally release for 5 minutes, then finish the release by setting to Venting.
The sauce will look too thin, but give it a stir and it will thicken up with the pasta and meat.
Serve Instant Pot One-Pot Spaghetti with Parmesan cheese garnish, and a side salad.