Peel and finely chop the garlic. Clean the chilli, cut lengthwise, wash and remove the seeds. Chop the pod finely. Mix vinegar, sugar, garlic and chili. Fold in oil in a thin stream. Season to taste with salt and pepper.
Clean, wash and dry zucchini and slice lengthwise into thin strips. Mix the courgettes carefully with the vinaigrette and arrange on plates. Pluck the mackerel fillets into pieces and spread on the salad. Ciabatta tastes good with it.