Place the fish, onions, vinegar, ginger, spices, wine and water into a pot. Bring gently to a boil and simmer 10 minutes.
Add the scallops and prawns and cook another 3 minutes.
Remove fish, bone and skin. Remove scallops and prawns.
Strain the cooking juice and set aside to cool for several hours to allow sediment to settle. Carefully pour off juices, leaving the sediment, and then strain several times through clean muslin. You should have about 3 cups of liquid left.
Melt gelatin in 1/2 cup of the liquid, cool to room temperature, then mix into the rest of the juices.
Pour a thin layer of the gelatin mix into a 4-5 cup mold or dish. Refrigerate until set.
Flake the fish and cut the scallops into 3 or 4 pieces. Arrange a layer of the best looking flakes, scallops and prawns on the layer of gelatin. Spoon on more gelatin and return to fridge to set gelatin.
Continue building layers of seafood and gelatin until all are used up.