To make the Korean BBQ Sauce: In a small pot, combine all ingredients except the cornstarch and water. Bring them to a simmer over medium heat for 10 minutes.
In a small bowl, whisk together the cornstarch and water to make a slurry.
Whisk the cornstarch slurry into the barbecue sauce, and boil it until it thickens, about 2 minutes.
Remove the barbecue sauce from the heat and transfer it to a canning jar or another heatproof container. Set aside.
Prepare grill to high heat.
To make the wings: Pat the chicken wings dry with a paper towel, and then season them lightly with salt and pepper.
Grill the wings until they’re slightly charred on all sides and the internal temperature has reached 165 º F on an instant-read thermometer, about 15-20 minutes.
Brush the wings with a little barbecue sauce and cook for another 1-2 minutes.
Remove the wings from grill to a large bowl, and toss them with more barbecue sauce.
Garnish the wings with fresh scallions and serve hot.