01 - Adjust oven rack to center position and preheat to 375°F (190°C).
02 - In a large mixing bowl, combine cooked rice, shredded chicken, peas, diced carrots, celery, cheddar cheese, cream of chicken soup, sour cream, milk, melted butter, garlic powder, onion powder, black pepper, and kosher salt. Stir thoroughly to incorporate all ingredients.
03 - Spread the chicken and rice mixture evenly into a lightly greased 9x13-inch casserole dish.
04 - In a small bowl, mix panko breadcrumbs, parmesan cheese, and melted butter until evenly coated.
05 - Sprinkle the breadcrumb mixture evenly over the casserole.
06 - Place the dish in the preheated oven and bake uncovered for 30 minutes, or until topping is golden and filling is bubbling.
07 - Allow casserole to cool for 5 minutes before serving.