Pre-heat the oven to 180c.
Peel and slice the cucumbers lengthways, scrape out the seeds with a spoon and discard. Dice the cucumbers into 1cm cubes. Finally, dress the cucumbers in the mustard, honey, vinegar and finely chopped dill and set aside. Roll out the pastry enough to roll over a side of salmon.
Cut the fillet in half lengthways, Lay the fillet in the centre of the pastry, arrange the cucumber dressing on top of the salmon then lay the other half on top of this. Carefully roll the pastry tightly around the salmon to encase it all. Brush with the egg glaze and season the pastry. Place in fridge to set. After 15 minutes or so, place in the oven for 30 minutes until the pastry has cooked to a golden brown colour.