Cook the lentils in boiling water for about 10 minutes. Quench and drain well. Clean, wash and cut spring onions into rings. Wash, halve and core apples. 1 1⁄2 Cut apples into slices.
Peel and chop the rest.
Finely puree vinegar, salt, pepper, some sugar, oil and apple cubes. Dice bacon finely and fry until crispy. Fry onions and apple slices briefly. Mix with lentils and marinade. Leave to stand for at least 30 minutes.
Wash the lettuce leaves, shake dry and divide into four plates. Season lentil salad again and arrange on the salad.