Boil the lentils in ¼ l water with 1 teaspoon vegetable stock for 10 minutes, then strain and drain. Fry the onions and leeks in hot oil for 1 minute. Add 50 ml water, the remaining vegetable stock and apple cubes and cook for 1 minute.
Put everything with the lentils in a bowl, add the balsamic vinegar and chives and mix in. Fold in the cleaned lamb`s lettuce and serve immediately.