Preheat the oven to 190°C. Line a 23 x 33 cm metal baking dish with foil, leaving a 5 cm overhang on both short ends. Spray the foil with cooking spray. Place the fish in the dish in a single layer.
Combine the soy sauce, sherry, ginger and sesame oil in a small bowl. Spoon the mixture over the fish then fold the foil across the top to seal loosely. Bake for 8 to 10 minutes or until the fish is just cooked through.
Carefully lift the foil-wrapped fish from the baking dish and transfer the fish fillets to individual serving plates. Spoon the pan juices over the fillets, then sprinkle with the sliced spring onions.