Sprinkle the lentils briefly with cold water and allow to drain. Clean, wash and cut the leek into fine strips. Heat 1 tablespoon of oil. Sweat the leek in it. Add the lentils, deglaze with broth and cook for 10-15 minutes.
In the meantime, wash the fish fillets and pat them dry. Cut pieces a little bit smaller, salt. Heat 1 tablespoon of oil in a pan. Fry the fish fillets for about 8 minutes while turning. Season lentils with salt, pepper and vinegar.
Serve with the fish.