Put the cleaned fish in a large pan, pour in enough water to cover it and salt it well.
Add enough vinegar to make the liquid pleasantly sour.
Add one onion, sliced, the chilli, the bay leaves and the peppercorns.
Bring to the boil, then poach gently over medium heat for 15-25 minutes depending on the size of the fish, until the flesh comes away from the bones easily.
Meanwhile, cut the other 1-2 onions into thin rings and cook them separately in a little wine vinegar for a few minutes.
Carefully lift out the fish and lay it on a long platter.
Spread the cooked onion rings over it and drizzle with a little wine vinegar mixed with the poaching liquid.
Chill (in the fridge) for at least 2-3 hours before serving.
Based on: A jó házikonyha (a classic Hungarian cookbook), modernised. Calories and protein are estimated.