Season the fish fillet with salt and black and lemon peppers to taste. Using a sharp knife, cut about a one inch deep opening in the middle of the fillet from head to tail. Place the knife in the opening and cut a pocket to both sides of the opening. Unfold the pockets and spread the cheese in. Sprinkle finely chopped dill, chives and thyme on the cheese. Turn the upper side of each pocket on the cheese and herbs. If necessary, secure the opening with toothpicks. Sprinkle with lemon juice.