Cut half of the maties into fine strips, dice the rest finely. Wash apples, cut 2 slices from the middle for garnishing. Finely dice the rest of the apples. Sprinkle everything with lemon juice.
Peel and chop the onion. Drain the capers. Dice cucumber as well. Season all diced ingredients and capers with some pepper and mix. Arrange one lettuce leaf, one apple slice and matie in strips on plates.
Tartar on it. Serve garnished with parsley.