Combine the ☆ ingredients. Combine the wasabi with honey first, add lemon juice and salt, then finally the oil to emulsify.
Cut the cucumbers lengthwise into half, then into diagonal slices. Mince the onions. Combine in a bowl, rub with a pinch of salt (not listed), and let rest.
Slice the potatoes 1 cm thick and soak in water for 5 minutes. Toss in the frying pan, avoiding the pieces from overlapping each other. Add water.
Turn on the heat and once it comes to a boil, bring down the heat to the lowest, cover with a lid, and steam until the potatoes soften. Remove the lid once the potatoes are soft enough and evaporate any leftover water.
While the potatoes are still hot, mash roughly and combine with the ingredients from Step 1. Mash to your desired consistency. I like leaving chunks.
Remove the leaves of the persimmon and dice into 1 cm.
Once the potatoes have cooled, combine the tightly squeezed cucumbers and onions, persimmons, and toss.