Preheat oven to 400°F. Grease a 9x13-inch baking dish.
Toss potatoes with half the oil, half the ranch, and half the spices.
Spread potatoes in the dish. Roast 20 minutes, stirring once.
Mix chicken with remaining oil, ranch, and spices until coated.
Add chicken to the pan. Stir with potatoes to combine.
Bake 20 to 25 minutes, until chicken hits 165°F and potatoes are tender.
Cook bacon in a skillet until crisp. Drain and crumble.
Top casserole with cheddar and bacon. Bake 5 to 8 minutes to melt.
Rest 5 minutes. Scatter green onions and add dollops of sour cream.