Preparing the mackerel...

Fillet the whole mackerel and trim up each fillet.
With a sharp knife, slice down each side the central bone and remove with fish tweezers. Put the Colman’s English mustard into a small piping bag and then pipe a thin line in the gap where bones were. Leave to one side.
Take all crusts off the bread and roll out as thin as you can with a rolling pin.
Place the mackerel fillet in the middle of the bread sheet and roll over one side and brush with a little egg wash. Seal the bread where the two sides meet and trim off any excess. Wrap tightly in cling film and return to the fridge to set.
Using a frying pan, shallow fry in the rapeseed oil to get an even golden brown colour all over; this will take about 3-4 minutes. Remove the mackerel from the rapeseed oil and leave to drain on a j- cloth.
Cut the mackerel three even sized shapes.

The garnish...

Slice the smoked streaky bacon into 1 cm slices and then cut across the slices to form 1cm lardons. Cut the cherry plum tomatoes in half length ways.
Trim the leaves from the little gem lettuce and wash in cold water. Drain the leaves in a colander and then cut each leaf into quarters. Cut each gem leaf again into 4-5cm lengths.
Heat a non stick frying pan add a little of the remaining rapeseed oil.
Add the smoked bacon lardons and fry gently until golden brown and then add the cherry tomato halves. Continue cooking on a gentle heat until the tomatoes start to soften slightly. Remove the smoked bacon and cherry tomato mix from the frying pan on to a j-clothed tray.

To serve...

In opposite corners of the serving plate, make two small piles of the smoked bacon and cherry tomato mixture and top with the washed pieces of little gem lettuce.

Spoon the juices from the smoked bacon and cherry tomato mixture on and around the mackerel and salad.