*To make in the Instant Pot:
Press the "saute" button and wait a couple minutes for the insert to heat up. Add the oil, carrots, celery, onions and garlic and saute until tender, about 5 minutes.
Add the tomatoes and cook for a minute.
Add stock, lentils (I tested with French green and black), raw brown rice, thyme and salt. Press the "Keep Warm/Cancel" button to turn the machine off. Secure the lid on top of the insert and lock closed. Make sure the vent is closed. Press manual and make sure it's on High Pressure. I cooked it for 12 minutes and thought that was perfect. The Instant Pot will take a few minutes to come up to pressure, so it will say ON for a few minutes. Once the machine is done cooking, you can manually release the pressure or opt for natural release. Check the manual for an explanation of both.