For the Spicy dipping sauce:
In a small bowl, mix together the mayo, hot sauce, black pepper and optional wasabi powder. Set aside.
Prepare a large cast iron skillet on high heat. ( you can also grill the peppers on an outdoor gas grill ~ make sure the grill is very hot )
Toss the Shishito Peppers with the oil and salt. Add them to the hot skillet and spread them around evenly. Don't touch them once you have placed them in the pan. Turn them after a minute or sooner ~ when they have charred and blistered. I tend to turn them twice to get 3 sides of the pepper nice and charred. Remove them from the pan and serve immediately with Spicy Dipping Sauce*.