Combine chicken, salsa verde, oil, cumin and salt in a 6-quart slow cooker. Cover and cook on Low until an instant-read thermometer inserted in the thickest part registers 165°F, about 3 hours, 30 minutes. Remove the chicken and shred, using 2 forks. Return the shredded chicken to the cooker; stir well to combine. Cover and continue cooking for another 30 minutes. Top with sliced jalapeño, cilantro and/or lime juice, if desired.