There are several varieties of mackerel, but the one I've encountered most frequently in Hungary is the Atlantic mackerel, Latin: Scomber scombrus. At 19 mcg/100 grams, its vitamin B12 content is more than 300% of our daily requirement! Mackarel is a great source of protein and also contains other B vitamins, selenium and magnesium. It's very tasty and has a distinctive taste, especially when smoked. It does not need much further seasoning, its at its best when eaten with fresh herbs, onions, pickles or acidic elements

To make the pickled onions, combine the water, vinegar, honey and salt in a saucepan and bring to a boil. Place the onion slices in a heatproof bowl and pour the hot vinegar over them and leave to soak. After 5-10 minutes the mixture will turn turn a lively shade of pink. The longer it soaks, the better it will taste. It can be eaten with many things, and is also a great garnish for your dishes. It will keep for a long time in the fridge if kept in a jar. Peel the skin off the mackerel (if it has any) and tear the flesh into larger pieces. Mix thoroughly with the mayonnaise, lemon juice, add salt and pepper to taste. Put the cucumber in a bowl, top with the smoked fish, sprinkle with the spring onion greens and the pickled red onion, and grate a little lemon zest over the top. Serve with some cooked cereals (e.g. buckwheat) or boiled potatoes with dill.