For the flaxseed crepes, whisk the egg with milk, whole wheat flour, 1 pinch of salt and flaxseed in a bowl until well blended. Let the dough rest for about 10 minutes.
Meanwhile, wash and dice the cucumber. Dice the feta cheese as well. Mix cucumbers with feta cheese and arugula and season with salt and pepper Heat oil in a pan.
Put the batter in the pan and fry a golden brown crepe on both sides. Spread the feta cheese and cucumber filling on top.
Season again if necessary and roll up the crepe.