Put a large piece of cheesecloth dipped in oil in an oiled roasting pan.
Season fish inside and out and place on top of cheesecloth.
Cut bacon slices into halves and arrange on top of fish.
Add boiling water to depth of 1 inch.
Place onions around fish.
Cover pan and bake in preheated very slow oven (200°F.) for 8 hours, or at 250°F.
for 6 hours until bones disintegrate.
Lift out fish carefully.