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