First make the Agadashi by placing the two sheets of Kombu in the cold water in a pot. Slowly bring to a very gentle simmer (do not allow to boil or the kombu will turn the liquid cloudy) and then turn off and let stand for 5 minutes.
Remove the Kombu and then bring the liquid to the boil, add the bonito flakes and turn of and allow the bonito to settle to the bottom of the pot for about 10 minutes then pass through a fine strainer. Then add the mirin and light soy and keep hot.
Halve, peel and quarter the avocados and set aside.
Heat the oil in a wok.
Combine the flour with the egg yolk and mix in enough ice water to make a batter.
Dust the avocado halves in a little flour and dredge in the ice-cold batter and place into the hot oil two at a time and cook until crunchy.
Drain on paper towel.
Place a tablespoon of diakon in each of 4 small Japanese bowls, divide the agadashi stock between each bowl and then place two pieces of tempura avocado in each and garnish with shisu cress.