Heat the oven to 400 degrees. Grease a casserole dish.
Stir-together the soup, sour cream, and cooked chicken, and spread into the greased casserole dish.
Crumble a sleeve of Ritz crackers, mix with the melted butter, and sprinkle over the chicken mixture.
Garnish the crumb topping with poppy seeds.
Bake at 400 degrees for 30 minutes.