To make the sautéed lentils, heat the oil in a saucepan and fry the shallot, carrot and bay leaf until they begin to turn golden-brown. Add the lentils and the cold chicken stock, give everything a good stir, and leave to cook for 20-25 minutes, or until the stock has reduced in volume. Remove the bay leaf and season with salt and pepper. Keep warm.
For the mayonnaise, put the egg yolk, lemon juice, mustard and sea salt into a mixing bowl and lightly blend together. Gradually whisk in the oils, a little at a time, until you have produced a thick and silky smooth mayonnaise. Mix in the parsley.
For the fish, pour 1cm/½in of olive oil into a large non-stick frying pan, placed over a medium heat, or you can also use a deep-fat fryer heated to 170C/340F (Caution: hot oil can be dangerous. Do not leave unattended).
Coat the pieces of hake in flour, knock off the excess and then coat well in the beaten egg. Place into the hot oil and fry for about four minutes on each site, depending on the thickness of the fish, until golden-brown. Lift onto kitchen paper, and leave to drain.
Finally, add the spinach to the lentils and allow it to wilt for a minute or so.
To serve, divide the lentils among the serving plates. Place the hake on top. Add a tablespoon of lemon mayonnaise on top of the fish, and finally some of the jamón pieces.