Julienne all the vegetables, keeping only the green part of the courgettes. Sauté the vegetables for a few minutes with a bay leaf. Separately, pour the wine, vinegar and sugar into a saucepan and bring to a boil. Leave to boil for a couple of minutes, then add the sautéed vegetables and bring back to a boil. Leave to cool. Separately, slice the mackerel fillet into three equal parts, flour it and fry it in boiling peanut oil until golden. Place the vinegar, wine and vegetable mixture in a small bowl and place the fried mackerel fillets on top. Leave to rest in the refrigerator for one night. To serve, spread some red cabbage sauce on a dish, then place a layer of vegetables and the mackerel fillets on top. Garnish to taste.