Preheat your oven to 250 C. Lightly grease a 9x13 baking dish with butter.
In a large mixing bowl, combine the olive oil, salt, ranch dressing mix, and pepper. Add the cubed potatoes and toss well to coat all the potatoes. Spoon the potatoes into the backing dish, leaving as much of the oil mixture in the bowl. Roast until the potatoes are crispy, about 1 hour, stirring every 15 minutes.
While the potatoes are roasting, add the chicken to the bowl with the oil mixture and toss to coat and set aside. In a separate bowl, mix together the cheese, bacon, and spring onion and set aside.
When the potatoes are crispy, remove from the oven and lower the temp to 200 C. Add the chicken to the top of the potatoes then top that with the cheese mixture and bake for another 15-20 minutes or until the cheese is melted. Remove from the oven and let this rest for 10 minutes. Serve with sour cream or ranch dressing.