Add chicken breasts to the bottom of the Instant Pot or pressure cooker. Dice a yellow onion, green bell pepper and jalapeño and add to the pot with the chicken.
Stir everything together and put the lid on the Instant Pot. Set it to seal and use the chili setting, if you have it, or manually pressure cook on high for 20 minutes.
Allow a natural release for 10 minutes or quick release by switching to vent. Take the pieces of chicken out, put them on a plate and shred with two forks.