In a large bowl, combine the sweet chili sauce, soy sauce, rice vinegar, sesame oil, minced garlic, and grated ginger. Mix well to create the marinade.
Add the chicken thighs to the marinade, ensuring they are well coated. Cover and refrigerate for at least 30 minutes, or up to 2 hours for more flavor.
Preheat your grill or a large skillet over medium-high heat. Remove the chicken from the marinade, allowing excess marinade to drip off.
Grill or cook the chicken for about 6-7 minutes per side, or until the internal temperature reaches 165°F and the chicken is nicely caramelized.
While the chicken is cooking, pour the remaining marinade into a small saucepan. In a separate bowl, mix the cornstarch and water until smooth, then add to the saucepan.
Bring the marinade to a simmer over medium heat, stirring constantly until it thickens, about 2-3 minutes.
Once the chicken is cooked, remove it from the heat and let it rest for a few minutes. Slice the chicken into strips.
Serve the sliced chicken over cooked rice or noodles, drizzled with the thickened marinade. Garnish with sesame seeds and sliced green onions.