Preheat oven to 375 degrees or prepare grill for medium-high heat.  Take two sheets of heavy duty foil, generously dot with butter, top with fish, dust fish with Old Bay Seasoning, top with lemon slices and dill, dot with remaining butter.  Seal foil completely. Put in the oven or on the grill, cook for 15 - 20 minutes, foil will puff up - poke two holes in the foil.  Continue to cook for 5 minutes.