In a small bowl, whisk together cornstarch and water until smooth. Set aside.

In a medium saucepan over medium heat, combine the brown sugar, soy sauce, garlic, rice vinegar, ginger, honey, and sesame oil. Add the cornstarch mixture and stir constantly until the sauce comes to a simmer. Continue cooking, stirring frequently, until thickened to a dark, glossy syrup, about 2-3 minutes.

Remove from heat and let cool completely. To speed cooling, place the saucepan in the refrigerator for 15-20 minutes.

Once the sauce is cool, place the cubed chicken in a large resealable plastic bag. Pour half of the sauce over the chicken, seal the bag, and gently massage to coat evenly. Refrigerate for at least 30 minutes (or up to 2 hours for deeper flavor). Reserve the remaining sauce for basting.

Preheat your grill to medium heat (about 350°F). If using bamboo skewers, soak them in water for 30 minutes before threading.

Thread the marinated chicken onto the skewers, leaving a small gap between pieces. Lightly oil the grill grates.

Place skewers on the grill and cook, turning every 3-4 minutes, until the chicken is cooked through and reaches an internal temperature of 165°F, about 20-30 minutes total. During the last few turns, brush the skewers with the reserved teriyaki sauce.

Remove skewers from the grill and let rest for 2 minutes. Garnish with sesame seeds and chopped green onions, if desired. Serve over steamed rice.