Turn the Instant Pot to the Saute function, and heat the oil.
Add the onions, carrots, celery, and garlic. Saute until the onions are translucent.
Add 1 cup of the broth to deglaze the pot, scraping everything off the bottom. Turn off the Saute function,
Add the remaining stock, thyme, bay leaf, salt and pepper. Stir in the split peas.
Put the lid on, turn the knob to Sealing, and set to High Pressure for 15 minutes.
When the time is up, do a quick release. When venting is complete, remove the lid and stir the soup. If desired, for a smoother consistency, blend with an immersion blender. Garnish with chopped parsley.