Dab fillet dry, wrap in foil and freeze for about 1 hour.
For the mayonnaise, whisk the egg yolk, mustard and vinegar with the whisks of the mixer for about 1 minute. Stir in 200 ml oil, first drop by drop, then in a fine stream. Season mayonnaise with salt, pepper and lemon juice and chill.
Sort the arugula, wash and drain well. Finely slice the parmesan. Take the meat out of the freezer and cut it into very thin slices with a very sharp knife across the fibre. Distribute the meat on plates, slightly overlapping.
Season with a little salt and freshly ground pepper. Pour mayonnaise into the piping bag and spray on top in a grid pattern. Serve with rocket salad and parmesan. Ciabatta tastes good with it.