Place the chicken breasts in the Instant Pot and sprinkle evenly with the ranch seasoning and au jus mix.
Load the Pressure Cooker
Add the sliced pepperoncini, pepperoncini juice, and butter over the chicken.
Pressure Cook
Seal and cook on high pressure for 13 minutes, then carefully perform a quick release.
Shred and Stir
Remove the chicken and shred with forks while hot, then stir back into the cooking liquid.
Preheat and Prep
Preheat the oven to 350°F and lightly grease a 9x13 baking dish. Slice the slider buns in half and place the bottoms in the dish.
Assemble
Spread Dijon mustard over the buns, layer provolone on top, then spoon the shredded chicken generously over the cheese. Scatter extra pepperoncini over the top, if using.
Top and Butter
Add the top halves of the buns and brush with the melted butter mixed with garlic powder and parsley.
Bake
Cover loosely with foil and bake for 15 minutes, then uncover and bake 5 more minutes, until the cheese is melted and the tops are lightly golden.
Rest and Serve
Let rest for about 5 minutes before slicing apart and serving.
Notes
Chicken thighs can be used in place of breasts for extra juiciness.
If using frozen chicken breasts, add 2 extra minutes to the pressure cook time.
Store leftovers in an airtight container in the fridge for up to 3 days; reheat in the oven at 325°F. Do not microwave.