Soak mushrooms for 30 minutes, drain then remove and discard stalks, and chop the remainder.
Peel cucumbers and cut into 1cm pieces. Scrape seeds out and discard. Parboil cucumber shells for 1 minute. Rinse in cold water, drain and dust inside with a little cornflour.
Drain water chestnuts and discard liquid. Mash and add rice flour, a dash of sesame oil and ¼ teaspoon each of sugar and salt. Add carrot and mushrooms and mix well. Stuff cucumber circles and place on a plate. Steam in steamer, covered, for 15 minutes.
In a separate saucepan, mix a dash of oil with pepper tot aste and remaining sugar and salt. Add remaining cornflour. Stir in stock or water until smooth. Heat until thickened and pour over the cooked cucumber pieces.
