Mix hot water with wasabi powder and allow 5 minutes to activate, or combine prepared wasabi and mayonnaise.
Mix in tuna, celery, salt, wasabi, and mayonnaise together in a mixing bowl.
Peel cucumbers (optional). Slice each cucumber crosswise into 5 or 6 pieces each about 1-2 inch thick.
Scoop out the centers using a melon baller or a spoon. Stuff cucumber cups with prepared tuna.
Squeeze fresh lime juice on each cup. Garnish with fresh cilantro.