For pickled roast herrings, briefly bring vinegar and water to a boil. Add peppercorns, mustard seeds and bay leaves. Peel onions and cut into thin rings.
Wash and dry the herrings. Sprinkle with lemon juice. Rub inside and out with salt. Dredge herrings in flour and pat down a little.
Heat oil in batches in a frying pan. Sauté herrings in it for 6 to 8 minutes on each side.
Layer fried herrings and onion slices in a bowl, let cool a little.
Pour the still hot vinaigrette over the fish so that they are completely covered. Cover and leave to marinate for about 2 days.
Drain the liquid from the herrings and arrange on plates.
Decorate the pickled herrings with pickled gherkins or tomatoes and lettuce leaves.