Soak wooden skewers in a shallow bowl of water. Cut chicken into bite sized pieces. Cut scallions into 2-3 inch pieces.
Make the sauce: Whisk soy sauce, brown sugar, ginger, garlic, honey, sesame oil and rice vinegar in a saucepan over medium heat. Bring to a boil, whisking constantly.
Lower the heat. Combine cornstarch and 3 Tbsp. of water in a small bowl. This is a slurry. Pour the slurry into the sauce and whisk to combine. Simmer the sauce until thickened.
Remove sauce from heat and pour into a large bowl. Place chicken in the sauce and toss until well coated.
Preheat grill to 400 degrees. Thread the chicken and scallions onto the wooden skewers. Grill 10 minutes on one side. Flip and grill another 8-10 minutes, until desired degree of char is achieved and an internal temperature of 165 degrees is reached. Baste the chicken with additional teriyaki sauce for extra flavor. Garnish with sesame seeds, if desired