Push the SAUTÉ button on the instant pot. Add oil and onion, and cook stirring, until the onion is soft. (This step is optional- it just develops the sweetness in the onion flavor. If you choose to skip the sauté then just add the onion to the pot with the rest of the ingredients).
Add remaining ingredients, put on the lid, seal the pressure valve, and set to MANUAL or HIGH PRESSURE for 18 minutes.
After the cooking cycle is complete, let the pressure release naturally for at least 10 minutes, then twist the valve to release the remaining pressure.
Remove chicken from pot and shred it. Put it back in the pot, and if it tickles your fancy add some heavy whipping cream to make THIS soup even creamier and delicious.
