Cut thighs into large bite size chunks and cut onion into chunks. Put chicken and onions into pressure cooker. Mix all other ingredients together (except the cornstarch) well with a fork and pour on top.
Close the lid and steam valve and set Instant Pot to high pressure for 4 minutes. Do a natural release for 1 minute and carefully lift lid.
Put some of the hot liquid from pot in a small bowl with the cornstarch and whisk together, then add back into the pot and stir. Set Pot to saute and let bubble for a few minutes to allow sauce to thicken for 2-3 minutes. Serve over rice.