Drain the lentils. Clean the spring onions and cut into fine rings. Wash and chop the tomatoes. Pluck, wash and chop the parsley. Dice the sheep cheese. Mix everything carefully with the lentils. Mix vinegar, salt, pepper, mustard and oil into the dressing and add to the salad ingredients. Sprinkle with parsley. Mix well and let steep for about an hour. Goes well with grilled food or just on its own with bread.