Remove any bones from the fish with tweezers, cut in half, place on a baking tray lined with baking paper. Brush the fish with oil, season with salt. Mix the bread with all the other ingredients up to and including the egg whites, spread over the fish, press down lightly.
Mix the sweet potatoes with the oil and salt in a bowl, spread onto an oven tray lined with baking paper.
Bake the fish and fries for approx. 18 mins. in a (convection) oven preheated to 180°C.
In a bowl, mix the egg yolk, mustard, lemon zest and juice using a whisk. Add the oil drop by drop to begin with, then gradually more, stirring constantly to form a thick mayonnaise, then season.