Whoever invented aluminum foil did us a favor, for it has proved to be wonderful as a disposable receptacle in which to cook. The foil does not let any moisture escape. The fish loses a bit of its juices into the packet, but these mingle with the vegetables there and add flavoring to form a sauce that is lean, delicious and accentuates the moistness of the fish flesh. Foil steaming is one of my favorite methods of preparing fish, not only because of the florious taste and texture obtained, but because it is neat and clean. Once you open that package and place its contents on a plate, there is no pot or pan to clean. If you wrap the fish securely, the jelly-roll pan on which you put the fish to bake will not even be dirty.