Preheat oven to 375 degrees F. Spray a 9x13 baking dish with nonstick cooking spray. Add chicken to the bottom of the pan. Top with ham and then slices of swiss cheese. Set aside.
Make the Casserole Sauce
In a small pot, melt butter over medium heat. Sprinkle in flour and whisk to create a paste. Slowly whisk in chicken broth to avoid lumps. Bring to boil to thicken, then reduce to simmer. Stir in milk and seasonings. Taste and adjust seasonings. Remove from heat and pour over chicken, ham and cheese.
Make the Buttered Bread Crumbs
In a small nonstick skillet, melt butter. Sprinkle in breadcrumbs and seasoning salt. Stir to coat in butter and toast lightly. Remove from heat and sprinkle over the top of the casserole.
Cover the casserole with foil and bake for 25 minutes or until hot and bubbly. Serve by itself or alongside rice and salad.