Make sure the stainless steel insert is in your Instant Pot.
Press the "saute" setting and wait until the display shows HOT.
Cut chicken into 1" pieces. Season with salt and pepper.
Add oil to the pot and heat up.
Add onion, celery and garlic and saute for 2 to 3 minutes.
Add Italian seasoning and rice and saute for 2 minutes, stirring often.
Add ½ cup of water and deglaze the bottom of the pot by scraping any cooked-on bits with a wooden spoon. This is important as it will prevent the burn.
Add remaining water, seasoned chicken, frozen veggies and butter. Stir in.
Close the lid and turn the valve to "sealing" position (the newer IP models do it on their own). Press “manual” or “pressure cook” button. Set timer to 5 minutes. Make sure the IP is set to high pressure.
The IP will beep and start building up pressure. This can take 10 to 12 minutes.
Once the cooking cycle is done, press “cancel/off” button and let the Instant Pot release the pressure naturally.
Open the lid and stir the rice. You can add cheese and season with more salt and pepper if needed.