For ease in handling, wrap the whole fish in cheesecloth.
Add sliced onions and lemons to the bottom of the fish poacher or large skillet.
Place fish on top of onions and lemons.
Pour any amount of white wine over fish, then add enough water to cover about 1 inch above the fish.
Bring the liquid to boil, then reduce to a simmer. Cover. Poach for about 15 minutes until fish will flake when you put a fork to the end of it. The thicker the fish, the longer it will take.
Refrigerate. Garnish with cucumbers and limes just before serving.