In your Crock-Pot, add the water or broth, chicken thighs, au jus seasoning, and ranch dressing mix.
Layer the sliced onions and bell peppers on top of the chicken.
Pour in the pepperoncini juice, add the pepperoncinis, and place the butter in small dollops around the top.
Cook on Low for 6-8 hours, or on High for about 4 hours.
When the chicken is tender, use two forks to chunk it gently—try not to shred.
Remove ½ cup of the cooking liquid and whisk in 1 tablespoon of cornstarch.
Return the cornstarch mixture to the Crock-Pot and stir to thicken the sauce.
Serve over mashed potatoes, rice, or on a hoagie roll topped with provolone cheese.