Preheat oven to 400°F (200°C). Lightly grease a 9x13 inch baking dish or line a large sheet pan with parchment paper.

In a large bowl, toss the cubed potatoes with 1 tablespoon of olive oil, 1/2 tsp salt, and 1/4 tsp pepper. Spread them in an even layer in the prepared baking dish.

Roast the potatoes for 15 minutes to give them a head start. Meanwhile, toss the cubed chicken with the remaining 1 tablespoon of olive oil, garlic powder, paprika, and remaining salt and pepper.

Remove the dish from the oven and push the potatoes to one side. Add the seasoned chicken cubes to the empty side of the dish. Return to the oven and roast for another 10 minutes.

While the chicken and potatoes roast, prepare the topping: In a medium bowl, combine the ranch seasoning mix, milk/buttermilk, and softened cream cheese. Whisk until smooth. Stir in the cheddar and Parmesan cheeses.

Remove the dish from the oven. Spoon the cheese and ranch mixture evenly over the chicken and potatoes, ensuring the chicken is mostly covered. Return to the oven and bake for an additional 10-15 minutes, or until the chicken is cooked through (internal temperature 165°F) and the cheese topping is bubbly and lightly golden brown.

Let rest for 5 minutes before serving. Garnish with fresh parsley if desired.