Defrost the fish. Clean, wash and roughly dice the leek. Peel and wash carrots and cut them into small pieces. Heat 1 tablespoon of oil in a saucepan, fry the leek and carrots in it.
Deglaze with broth, add lentils and cook covered over medium heat for about 35 minutes. In the meantime wash the fish, dab dry and sprinkle with lemon juice. Season with salt and pepper. Put flour, breadcrumbs and eggs in 1 deep plate each.
Beat the eggs. Cut the fish into 8 pieces and turn it first in flour, then in egg, then in breadcrumbs and finally one more time in egg. Bring cream to the boil and stir in mustard. Add mustard cream to the lentils and cook for another 10 minutes.
In the meantime, heat 2 tablespoons of oil in a pan and fry the fish for 3-4 minutes on each side until golden brown. Take out. Season lentil vegetables with salt, pepper and a few drops of lemon juice. Arrange lentil vegetables and fish on a plate.
Serve garnished with lemon and parsley. Parsley potatoes taste good with it.