01 - Preheat oven to 375°F. Grease a 9x13-inch baking dish with butter or cooking spray.
02 - In a large bowl, whisk together cream cheese, milk, Dijon mustard, sour cream, garlic powder, onion powder, salt, and black pepper until smooth and well combined.
03 - Fold in the diced chicken, ham, and 1 cup of shredded Swiss cheese until evenly distributed throughout the sauce.
04 - Spread the chicken mixture evenly into the prepared baking dish. Sprinkle the remaining 1 cup of Swiss cheese over the top.
05 - In a small bowl, combine panko breadcrumbs, melted butter, and Parmesan cheese. Mix until all breadcrumbs are evenly coated with butter.
06 - Sprinkle the breadcrumb mixture evenly over the casserole. Bake uncovered for 30 to 35 minutes, or until the top is golden brown and the casserole is bubbling around the edges.
07 - Remove from oven and let rest for 5 minutes to set. Garnish with chopped parsley if desired. Serve hot while cheese is melted and bubbly.