Preheat the oven to 350°F (175°C).
In a large mixing bowl, combine the cooked chicken, diced ham, 1 cup of shredded Swiss cheese, cream of chicken soup, milk, garlic powder, onion powder, black pepper, and salt. Mix well until all the ingredients are evenly coated.
Transfer the mixture into a greased 9x13 inch baking dish. Spread it out evenly.
In a separate bowl, mix the breadcrumbs with melted butter until they are well coated.
Sprinkle the breadcrumb mixture evenly over the chicken and ham mixture in the baking dish.
Top with the remaining ½ cup of shredded Swiss cheese.
Bake in the preheated oven for 35-40 minutes, or until the casserole is bubbly and the top is golden brown.
Once cooked, remove from the oven and let it cool for 5-10 minutes before serving.
Garnish with chopped parsley before serving.