Add 1 cup of water and a half a bottle of the barbecue sauce in the bottom of the Instant Pot.
Add 1/2 onion which is chopped into large chunks.
Top with the chicken breasts and coat the chicken with the sauce in the pot. Place the top of the Instant Pot and set on the seal, and set high pressure for 20 minutes.
You can use either fresh or frozen chicken, the pressure cooker will adjust time, based on the coldness of your chicken.
When the timer is done allow the pressure cooker to release its steam naturally (10 minutes).
Remove the lid and with two forks shred chicken.
Add additional barbecue sauce to the shredded chicken or the sauce in the pressure cooker and mix.