Turn your Instant Pot to Saute and add the olive oil, onion, bell peppers and salt. Saute for 3-4 minutes or until the vegetables are softened. Add the marinara, pesto and chicken. Cook thawed chicken on high pressure for 12 minutes. (Cook frozen chicken on high pressure for 20 minutes.) Turn the pressure valve to “Vent” to release all of the pressure.
Remove the chicken breasts from the pot and place on a plate or cutting board. Shred the chicken using two forks.