Preheat oven to 450°F. Spray a 9×13-inch baking dish with nonstick cooking spray.

Prepare potatoes: In a large bowl, mix diced potatoes with ¼ cup ranch dressing, salt, and pepper. Transfer to the prepared baking dish, spreading them out evenly.

Bake potatoes: Place the dish in the oven and bake for 30 minutes, stirring every 10 minutes.

Prepare chicken: While potatoes are baking, in the same bowl, toss the chicken cubes with the remaining ¼ cup ranch dressing, salt, and pepper.

Add chicken: After the potatoes have baked for 30 minutes, remove the dish from the oven and reduce the oven temperature to 400°F. Evenly distribute the marinated chicken over the potatoes. Cover the dish with aluminum foil.

Bake chicken: Return the dish to the oven and bake for an additional 20 minutes, or until the chicken is fully cooked (internal temperature of 165°F).

Add toppings: Remove the foil and sprinkle the shredded cheese, crumbled turkey bacon, and diced green onions over the chicken and potatoes.

Final bake: Return the dish to the oven and bake uncovered for 8–10 minutes, or until the cheese is melted and bubbly.

Serve: Allow the casserole to rest for a few minutes before serving.