Start by combining the buffalo sauce, olive oil, ranch seasoning, and black pepper in a small bowl. Mix it well until smooth. This sauce will coat both the potatoes and chicken, infusing them with bold flavor.
Toss the diced potatoes with half of the buffalo mixture. Spread them evenly on a lined baking sheet and roast at 425°F for 60-70 minutes. Flip them halfway through so they get crispy on all sides.
Place the chicken pieces in a resealable bag and pour the remaining buffalo mixture over them. Seal and refrigerate for 30 minutes while the potatoes roast. This step ensures the chicken absorbs all that spicy, tangy flavor.
Spray your baking dish with cooking spray, then layer the roasted potatoes first. Add the marinated chicken on top. Bake for 18-20 minutes, stirring halfway through, until the chicken reaches an internal temperature of 165°F.
Sprinkle shredded cheddar, Monterey Jack cheese, and crumbled bacon over the top. Return to the oven for 5-10 minutes, just until the cheese melts and bubbles. Finish with chopped green onions, a dollop of sour cream, and extra buffalo sauce.