In a medium-sized saucepan, whisk together the sauce
Bring to a boil, stirring constantly until the sauce thickens slightly, about 1 minute.
Transfer a few tablespoons of sauce to a bowl to use for brushing the chicken.
Thread pieces of chicken onto the skewers, alternating with green onion pieces
Lightly oil the skewers, season with salt and pepper
Preheat a large skillet over medium-high heat (or ideally a grill)
Add the skewers and let cook for 4 minutes. Turn and brush the cooked side with the sauce. Cook for another 4 minutes.
Turn the skewer, brush with sauce, cook for 2 minutes and cover
Turn the skewer, brush with sauce, cook for 2 minutes and cover
Repeat turning, basting, and covered cooking 2 more times, for a total cooking time of 16 minutes.
Sprinkle the yakitori with sesame seeds. Serve immediately with rice.
Notes
As usual, the chicken cut of choice is boneless chicken thigh because it not only provides a juicier result but also greater tolerance to overcooking (since there's more juice inside)