In a large bowl, combine turkey, ham and cheese, set aside. In a saucepan, saute onion in butter until tender. Add flour, stir to form a paste. Gradually add cream stirring constantly. Bring to a boil, boil 1 minute or until thick. Add dill, mustard and nutmeg, mix well. For the topping, toss bread crumbs, butter and dill; stir in cheese and walnuts. Sprinkle over the casserole. Bake uncovered at 350 degrees for 30 minutes or until heated through. Submitted By MOOREFAM@ONE.NET On WED, 15 NOV 1995 135500 -0500