Place the cucumbers, edamame and green onions in a large bowl.
In a small bowl, whisk together the rice vinegar, tamari, maple syrup (if using), ginger, lime juice and wasabi powder (if using). Add a little water if needed.
Pour the dressing over the vegetables and toss gently to combine.
Refrigerate for 15–20 minutes to allow the flavors to blend.
Garnish with sesame seeds, if desired and serve chilled.