Heat the oil in the pressure cooker over medium-high heat. Add the onions, peppers, and cumin and saute for 2 to 3 minutes to soften the onions. Add the lime juice, salsa, and stock, stirring to combine. Put the chicken breasts in the sauce, sticking the chicken to fit. Lock the lid in place and cook at high pressure for 5 minutes.
Release the pressure naturally and remove the lid, tilting the pot away from you to avoid the escaping steam. Remove the chicken from the pot and transfer to a cutting board. Skim any excess fat from the sauce. Pull the chicken apart into shreds or cut into 1/2 inch dice. If not using right away, refrigerate the sauce for up to 4 days or freeze in airtight containers for up to 6 months. Cool the chicken and refrigerate for up to 3 days or freeze for up to 3 months.