Mix the remoulade ingredients together and season well.
Mix the flour with half the Cajun spice mix and put on a plate. Mix the breadcrumbs with the rest of the spice mix and put on another plate.
Dip the prawns first in the flour, then the egg, then the breadcrumbs. Heat 3cm oil in a large, wide frying pan. Cook the prawns for a minute on each side, until golden. Drain on kitchen paper.
Split the bread ¾ of the way through. Spread all over with remoulade and add some lettuce. Pile on the prawns and eat.