Eggs hard boil, shell and slice finely. Cheese grate on a coarse grater. Separate the parsley leaves and chop. With half of a lemon grater, remove the zest from the flesh of a whole lemon and squeeze the juice.
In a bowl, mix eggs, cheese, dry mustard, parsley, zest and lemon juice. Season with salt and pepper.
Fish make 3 deep diagonal cuts on each side. Put inside the fish cooked stuffing. Place the fish on the grill by wrapping each in a sheet of foil, and place in a preheated 180 °C oven for 20 min.