Add the diced onion, beef, mushrooms, broth, soy sauce, rice vinegar, hoisin sauce, and ginger into a large resealable freezer bag. Squish to mix everything together. Take out the extra air from the bag, seal, and freeze.
On the day you want to serve the soup, take the bag out of the freezer to thaw.
Set the Instant Pot to high pressure and set for 15 minutes.
Lock the lid and be sure the vent is closed.
Vent the pressure from the Instant Pot.
Add the noodles, making sure that they are completely submerged. Close and lock the lid on the Instant Pot, ensuring that the vent is closed. Set the Instant Pot to 2 minutes.
Once the 2 minutes is up, allow the pressure to release naturally for 10 minutes. Afterwards, open the vent to release the remaining pressure.