In a saucepan, put the washed lentils, parsley and bay leaf (tied together with a thread), carrots cut lengthwise. Fill with water, bring to a boil, and cook for 30 minutes.
Boil the chicken fillet, cut into strips.
Cut the onion into half rings.
Whisk the butter with vinegar, salt and pepper.
Pour into a bowl with the onion and mix.
Discard the lentils on a sieve, remove the carrots and herbs. Put it in a bowl with onions, mix. Add the chicken and mix.
