Horseradish is tempered by mild, cool cucumber and yogurt.
Cut cucumbers into large chunks. Puree half the cucumber with yogurt, lemon zest, and horseradish in a blender until just smooth. Add remaining cucumber, and pulse until chunky, about 4 times. Season with pepper. Refrigerate until cold, about 1 hour. Stir well, and garnish with grated lemon zest and thinly sliced cucumber, if desired, before serving.
