Preheat the oven to 425°F (220°C).
Lightly grease a 9×13-inch baking dish with cooking spray or a small amount of oil.
Arrange the chicken breasts in a single layer in the prepared baking dish.
Sprinkle the ranch dressing mix evenly over the chicken breasts.
Sprinkle the halal-friendly au jus-style gravy mix over the ranch seasoning.
Distribute the sliced pepperoncini or banana peppers over and around the chicken.
Arrange the butter slices evenly over the chicken breasts.
Place the baking dish in the preheated oven and bake the Oven Baked Mississippi Chicken for approximately 25–30 minutes.
Check the thickest portion of each chicken breast with an instant-read thermometer. The chicken is safely cooked when it reaches an internal temperature of 165°F (74°C).
Remove the baking dish from the oven and allow the chicken to rest for about 5 minutes.
Spoon some of the buttery pepperoncini pan juices over each chicken breast before serving.