Preheat the oven to 350 degrees Fahrenheit (175 degrees Celsius) and grease a 9x13 inch baking dish.
In a large mixing bowl, whisk together the condensed cream of chicken soup, milk, garlic powder, onion powder, salt, and black pepper until smooth.
Fold the cubed chicken, cooked rice, and steamed broccoli into the soup mixture until evenly coated.
Stir in 1.5 cups of the shredded cheddar cheese.
Spread the mixture evenly into the prepared baking dish.
In a small bowl, combine the panko breadcrumbs and melted butter. Sprinkle the remaining 0.5 cup of cheese over the casserole, followed by the buttered breadcrumbs.
Bake for 30 to 35 minutes until the sauce is bubbling and the topping is golden brown.
Remove from the oven and let stand for 5 minutes before serving.