Step 1: Prepare the Potatoes and Chicken
Preheat your oven to 375°F (190°C). Generously grease a 9×13 inch (23x33cm) baking dish. Place the cubed potatoes in a large bowl. In a separate bowl, toss the cubed chicken with olive oil, 1 tsp garlic powder, onion powder, smoked paprika, salt, and pepper until evenly coated.

Step 2: Par-Cook the Potatoes (For Perfect Tenderness)
Place the cubed potatoes in the prepared baking dish. Cover tightly with aluminum foil and bake in the preheated oven for 20 minutes. This par-cooking step ensures the potatoes will be fully tender and creamy by the time the casserole is finished, without overcooking the chicken.

Step 3: Create the Luxurious Creamy Ranch Sauce
While the potatoes par-cook, make the sauce. In a large mixing bowl, whisk together the cream of chicken soup, sour cream, ranch dressing, chicken broth, minced garlic, dried dill, dried chives, and black pepper until the mixture is completely smooth and well-combined.

Step 4: Combine Chicken, Sauce, and Cheese
Remove the potatoes from the oven (leave the oven on). Carefully add the seasoned, uncooked chicken cubes to the baking dish with the par-cooked potatoes. Pour the creamy ranch sauce over the potatoes and chicken. Using a large spoon or spatula, gently fold everything together until the potatoes and chicken are evenly coated. Stir in 2 cups of the shredded cheddar cheese and all of the Monterey Jack cheese until distributed throughout the mixture.

Step 5: Apply the Final Cheese Layer
Smooth the mixture into an even layer in the dish. Sprinkle the remaining 1 cup of shredded cheddar cheese evenly over the top.

Step 6: Create the Buttery Panko Crust
In a small bowl, combine the Panko breadcrumbs, melted butter, chopped parsley, and ½ tsp garlic powder. Mix until the crumbs are evenly moistened. Sprinkle this mixture evenly over the cheese layer, covering the surface completely.

Step 7: Bake to Golden, Bubbling Perfection
Return the uncovered casserole to the oven. Bake for 35-40 minutes, or until the chicken is cooked through (internal temperature of 165°F / 74°C), the potatoes are fork-tender, the topping is deep golden brown, and the sauce is bubbling vigorously around the edges. If the topping browns too quickly, tent loosely with foil.

Step 8: Rest, Garnish, and Serve
Remove the casserole from the oven and let it stand for 10-15 minutes before serving. This rest is essential for the sauce to thicken slightly and for the casserole to set, ensuring perfect, clean servings. Garnish liberally with sliced green onions and fresh chives or parsley just before bringing it to the table. Drizzle with extra ranch dressing if desired.