Place gingerroot on several layers of damp cheesecloth. Gather edges of cheesecloth together, and squeeze cheesecloth bag over a small bowl. Set aside 3 tablespoons ginger juice; reserve remaining ginger juice for another use.
Combine 2 tablespoons ginger juice, soy sauce, sherry, lemon juice, and sugar in a shallow dish; add fish, turning to coat. Cover and marinate in refrigerator 20 minutes, turning fish occasionally. Remove fish from marinade; discard marinade.
Place fish on broiler pan coated with cooking spray, and broil 3 minutes or until lightly browned (do not turn). Brush oil over fish, and broil an additional minute or until fish flakes easily when tested with a fork. Place fish on individual serving plates, and drizzle remaining tablespoon ginger juice over fish.