Preheat the oven to 450°F. Prepare a 9"x13" baking dish by coating it with nonstick cooking spray.
Combine the cubed potatoes with salt, pepper, and ¼ cup of ranch dressing in a large mixing bowl. Stir well to coat the potatoes.
Spread the potatoes evenly in the prepared baking dish. Reserve the mixing bowl for later use. Bake for 30 minutes, stirring every 10 minutes, until the potatoes are almost fully cooked but not yet tender.
Meanwhile, in the same bowl, mix the cubed chicken with salt, pepper, and the remaining ¼ cup of ranch dressing. Set aside.
Once the potatoes have cooked for 30 minutes, remove the dish from the oven and reduce the oven temperature to 400°F.
Arrange the marinated chicken evenly over the potatoes in the baking dish. Cover tightly with aluminum foil (use oven mitts as the dish will be very hot).
Return the dish to the oven and bake for an additional 20 minutes, or until the chicken is fully cooked and reaches an internal temperature of 165°F.
Take the dish out of the oven and evenly top with shredded cheese, crumbled bacon, and diced green onions.
Place the dish back in the oven and bake for another 8-10 minutes, or until the cheese is melted and bubbly.