Preheat the oven to 350 degrees F (175 degrees C)
Lightly grease a 2-quart baking dish with cooking spray
Stir together cream cheese, sour cream, ½ cup Monterey Jack cheese, melted butter, pepperoncini brine, ranch dressing mix, and au jus gravy mix in a large bowl until well combined
Stir in milk
Fold in cooked noodles, chicken, and pepperoncini peppers until evenly coated
Spread mixture into the prepared baking dish and sprinkle with remaining ½ cup Monterey Jack cheese
Bake until hot and bubbly, 25 to 30 minutes
