Hit 'saute' on the Instant Pot.
Add in the oil, onion, garlic, bell pepper, and celery, along with a good sprinkle of sea salt.
Briefly saute the veggies for 30-60 seconds, just to bring out the flavor. You don't want to overcook the veggies, otherwise they will become mushy in the pressure cooker.
Stir in the oregano, rice, and water.
Hit 'cancel' to stop sauteing.
Close and lock the lid, making sure the steam release valve is set to 'sealing'.
Press 'manual' and set the time to 22 minutes. No need to press any other button, it will just take a few minutes to come to pressure and begin cooking.
After 22 minutes, let the Instant Pot naturally release pressure for 10 minutes (in other words, don't touch it until the screen reads LO10).
Open the lid, add in the parsley, and fluff the rice.
Season to taste and enjoy!