Cut fish into 4 equal pieces. Boil shimp until pink. Drain and cool. Cut chicken into pieces and score heavily to insure that chicken cooks in same time as fish. Cut mushrooms into 4 segments. Butter the center of a square of aluminum foil, place fish, shrimp, chicken and mushrooms top with butter and lemon slice. Sprinkle over this 1/2 tablespoon of sake. Fold up packet and crimp edges. Place in hot coals for 10 minutes or in 475 degree oven for 20 minutes. Serve with soy sauce if desired.