Wash duck breast fillet and dab dry well. Score the skin side several times with a sharp knife. Season with salt and pepper.
Heat 1 tsp. oil in a small ovenproof pan. First fry the duck breast on the skin side for 3-4 minutes. Turn and fry for 1-2 minutes more. Cook in the preheated oven (electric cooker: 175 °C/circulating air: 150 °C/gas: level 2) for approx. 15 minutes.
Remove the meat and wrap it in aluminium foil. Let it rest for about 10 minutes.
Meanwhile wash and halve the tomatoes. Clean, wash and shake dry the arugula. Peel onion and cut into fine rings. Mix vinegar, salt, pepper and 1 pinch of sugar. Fold in 3 tablespoons of oil.
Add onion.
Carefully mix the tomatoes, arugula and vinaigrette. Cut duck breast fillet into thin slices and arrange on plates with the rocket and tomato salad. Ciabatta tastes good with it.