Cut fish into 1-½-inch pieces. Marinate in sherry and vinegar for 2 hours. Make a batter of the flour, egg, water, and salt. Drain fish and dip pieces into the batter. Fry in hot oil until golden brown. Serve with Sweet-Sour Sauce.
Saute chopped onions and green pepper in the oil. Add ginger root, soy sauce, brown sugar, and 1 cup water. Boil for 1 or 2 minutes. Dissolve cornstarch in a small amount of cold water, and use it to thicken the sauce. Add the vinegar, then pour sauce over hot deep-fried fish and serve. Makes about 1-¼ cups.