Preheat oven to 350 degrees. In bowl, combine shredded cooked chicken, condensed chicken soup and Dijon mustard. Mix well and spread into casserole dish. Next top with shredded deli ham and then Swiss cheese. In separate bowl heat butter in microwave, when melted add the crushed Ritz Crackers and spread on top of casserole. Bake in preheated oven for 30 minutes until bubbly hot.