Dab meat dry and season with salt and pepper. Cook the lentils in boiling water for about 15 minutes. Heat the oil in a pan and fry the meat for about 10 minutes while turning.
Wash lettuce, shake dry and tear. Wash lemon, grate dry, halve and squeeze juice. Mix lemon juice, mustard, crème fraîche and olive oil, season with salt and pepper. Drain the lentils and rinse with cold water.
Wash the apples, grate them dry and quarter them, remove the core and cut the quarters into slices.
Mix lentils, salad and apples with the dressing. Cut the meat into slices and arrange on plates with the salad. Sprinkle with cress and coarse pepper.