Add ground beef and onion to the inner pot of the Instant Pot. Sauté until the beef is completely cooked.
Add in rotini and then top with tomatoes, tomato sauce, chicken stock and ketchup and mustard. Noodles should be covered with liquid.
Put the lid on the pressure cooker and turn the pressure valve to sealed. Set manual high-pressure time for 5 minutes, doing a natural pressure release for 4 minutes before letting the remaining pressure out.