Separate chicken wing flats from drumettes, if they aren't already. Add to a gallon-sized storage bag. Set aside.
In a small bowl, add wasabi powder and water. Whisk together until combined. Add to a medium sauce pan, along with honey, soy sauce, minced garlic. Whisk together. Add 2/3 cup to wings in bag, seal bag, and toss together to coat evenly. Let them marinade for 1 to 4 hours in the refrigerator. Save remaining sauce for later.
When the wings are ready, preheat your grill to 350 degrees. Drain wings from marinade and discard marinade. Cook wings for 10 minutes and flip to cook for 10 more minutes.
While wings cook, place leftover sauce on medium heat and bring to a boil and then reduce to a simmer to reduce by half. Remove from heat to cool and thicken.
Once wings are cooked, toss them in reduced sauce and let them sit for 5-10 minutes. Remove from sauce and then sprinkle with sesame seeds and chopped green onions. Serve immediately.