3 English cucumbers, peeled and cut in chunks
1/2 cup cold water
1/2 tablespoon white vinegar
3 teaspoons kosher salt, divided
For the wasabi cream:
1 1/2 teaspoons wasabi powder mixed with 1/2 teaspoon water to make a paste
1 ripe California avocado, peeled and pitted
1/2 tablespoon fresh lemon juice
1 (8-oz) container plain yogurt
2 finely chopped scallions
1 1/2 cups ice cubes
Garnish: finely chopped scallion greens
Purée cucumbers with water, vinegar, and 2 teaspoons kosher salt in a blender or food processor until smooth. Set aside.
Mix wasabi poser and water to make a paste. Mash together avocado, lime juice, and remaining teaspoon salt until smooth. Whisk in yogurt, wasabi paste, chives, and pepper to taste.
Just before serving, blend soup with ice until smooth. Serve topped with avocado cream and a sprinkle of chopped scallions.