Drain the tuna and capers. Finely puree the tuna, capers, salad cream and yoghurt. Season everything with salt, cayenne pepper, sugar and vinegar and chill
Wash the tomatoes and cucumber. Cut the tomatoes into large pieces. Halve cucumber lengthwise, cut into slices. Peel and chop onion. Wash parsley and chop roughly
Mix tomatoes, cucumber, onion and tuna sauce, season again. Serve with turkey cold cuts and sprinkle with parsley