1. Bring the chicken stock slowly to the boil with the piece of ginger in it.
2. Wash the cucumber and cut off the ends; run the potato peeler lightly over the skin to remove just the outermost tough layer.
3. Cut lengthwise into quarters and then into matchstick strips.
4. Cut the pork into very thin strips, place in a bowl and dust with the cornflour mixed with 1/2 tsp salt, rubbing it gently into the pieces of meat.
5. When the chicken stock comes to the boil, add the pork and simmer gently for 4 minutes; add the cucumber and simmer for a further 3 minutes.
6. Taste and correct the seasoning. Remove and discard the piece of ginger.
7. Serve very hot in heated soup bowls.