Start by making the teriyaki sauce. In a small bowl, mix cornstarch and water. In a medium saucepan, combine the rest of the sauce ingredients with the cornstarch/water mixture. Stir well and bring to a simmer. Cook until the sauce slightly thickens and turns dark brown. Remove from heat and let it cool completely (you can speed up the process by placing it in the fridge).

Once the sauce is cooled, place the cubed chicken in a large ziplock bag. Pour half of the sauce over the chicken, seal the bag, and gently shake to coat the chicken. Marinate the chicken in the fridge for at least 30 minutes. Set aside the remaining sauce for later use.

After marinating, thread the chicken onto skewers and preheat the grill to medium heat.

Once the grill is ready, place the skewers on the lightly oiled grill. Turn the skewers every 3-4 minutes until the chicken is fully cooked (internal temperature of 165°F), which should take about 20-30 minutes. During the last few turns, baste the chicken with the reserved teriyaki sauce.

Remove the skewers from the grill and serve with chopped green onions and a sprinkle of sesame seeds for an optional garnish.