Make the Sauce: In a bowl, combine buttermilk, mayonnaise, sour cream, ranch seasoning, Dijon mustard, lemon juice, garlic, and onion. Stir well. Add chopped sun-dried tomatoes, red pepper flakes, parsley, and hot sauce. Chill while prepping the rest.
Cook the Chicken: Season sliced chicken with salt, pepper, garlic powder, paprika, and chili powder. Heat oil in a skillet over medium-high. Cook chicken in batches for 6–8 minutes, stirring occasionally, until cooked through and lightly browned.
Toast the Rolls: Butter the inside of each roll. Toast them face-down in a hot skillet until golden and crisp, about 1–2 minutes.
Assemble the Cheesesteaks: Add a layer of cooked chicken to each toasted roll. Spoon on sauce and top with 2 slices of provolone. Melt the cheese under a broiler or by covering the pan for 1–2 minutes.
Serve: Serve hot with extra sauce on the side or pickled jalapeños if desired.