Clean the herrings and scrape the scales off the skin. Cut into fillets and lay the fish on a platter.
Spread the mustard on them and sprinkle them with the zest, salt, pepper and chopped dill.
Grill the fish on a very hot grill, first on the skin side for 1 minute, turn and grill on the other side for 1 minute.
Toast the mustard seeds in a dry frying pan.
Peel the shallot and chop it finely. Cut the strawberries into thin slices. Sprinkle the seeds, onion and berries onto the warm herring fillets.
Finally, drip on the vinegar, oil and chopped dill.