Preheat the oven to 350°F
Grease a 9×13-inch baking dish
Place 3 to 4 pounds of boneless, skinless chicken breasts or thighs in the dish
Sprinkle 1 packet ranch seasoning mix over the chicken
Sprinkle 1 packet au jus gravy mix over the chicken
Add 1/2 cup sliced pepperoncini peppers
Pour 1/2 cup pepperoncini juice over the chicken
Add 1/2 cup unsalted butter cut into slices
Cover the dish tightly with foil
Bake for 45 to 60 minutes, until the chicken is cooked through and tender
Remove the foil
Shred the chicken with two forks
Stir everything together in the dish
Top with 1 to 2 cups shredded mozzarella or provolone cheese, if desired
Bake uncovered for 5 to 10 minutes, until the cheese is melted
Serve hot over rice, mashed potatoes, noodles, or biscuits