In a small bowl whisk together mayonnaise, sugar, wasabi, vinegar, salt and pepper. Allow the dressing to sit refrigerated for at least 10 minutes or until ready to use to allow sugar to completely dissolve.
In a large bowl toss together cabbage, carrots and green onion.
Stir in dressing and serve immediately for a crisp coleslaw. .
The coleslaw with soften as it sits so it is best served immediately after adding dressing. It can be made a couple of hours ahead and tossed before serving if needed.