In a small mixing bowl or measuring cup, combine the ingredients for the marinade and stir well with a whisk or fork until well incorporated.
Place the pieces of chicken in a non-reactive container and add the marinade. Mix to coat really well, cover and place in the refrigerator to marinate for a couple of hours, or better yet, overnight.
Place skewers to soak in cold water for about 30 minutes before you start building your kebabs.*
Preheat your outdoor grill to medium-high.
Skewer the pieces of chicken onto 4 bamboo sticks; transfer the marinade to a small saucepan and bring it to a boil over medium heat, then simmer until reduced and thickened, about 5 minutes.
Place the chicken skewers on the grill, turning them every 2 to 3 minutes, brushing them lightly with the reduced marinade each time, until the meat is cooked through, about 10-12 minutes total.
Remove the cooked skewers to a plate, brush them generously with more of that reduced marinade and garnish with chopped green onions if desired; serve without delay.
*As it stands, the recipe is fairly hot and spicy; adjust the amount of pepper flakes and cayenne pepper to suit your own personal tolerance to heat. Omit if you don't care for heat at all. *There's plenty of marinade to marinate twice the amount of meat, so don't hesitate to double that up if feeding a crowd, or people with a larger appetite! *You could also thread the chicken onto the bamboo sticks prior to marinating them and place the finished skewers in a shallow baking dish that's long enough to accommodate them to marinate overnight, thus eliminating the need to soak the skewers.