Season chicken with vinegar, salt, pepper and oregano. Marinate a few hours if time permits.
Set the Instant Pot to saute, when hot add the oil and the chicken to brown on both sides, about 4 minutes on each side.
Add the tomatillo salsa, 2 tablespoons of the cilantro and jalapeno, cover and cook on high pressure 20 minutes, until the chicken is tender. When the pressure releases, garnish with cilantro and serve over rice if desired.
Slow Cooker Directions:
Place ingredients in the slow cooker and cook low 6 hours or high 3 hours.
Stove Top Directions:
Follow same directions, add a little water and cook covered on low until chicken is very tender, 30 to 40 minutes.