Very thinly slice cucumbers crosswise with slicer; toss with 1 teaspoon salt and drain in a colander 15 minutes. Rinse cucumbers under cold water, then squeeze handfuls to remove excess water; pat dry. Stir together wasabi powder and water in a bowl and let stand 5 minutes. Add vinegar, sugar, and soy sauce, whisking until sugar has dissolved. Add cucumbers and toss well.