Drain and flake tuna fish. Slice the eggs. Drain the mandarin oranges and olives and slice olives. Mix these ingredients together lightly. For dressing blend lemon juice and Soya sauce into oil and season with salt, pepper and sugar. Pour over the salad and leave to marinate in the refrigerator for 10 minutes. Divide the salad between 4 glass dishes and garnish with sprigs of parsley.