Preheat your oven to 400°F (200°C).
In a large bowl, whisk together the sweet chili sauce, soy sauce, honey, rice vinegar, minced garlic, grated ginger, sesame oil, black pepper, and red pepper flakes until well combined.
Add the chicken thighs to the bowl and toss to coat them evenly in the marinade. Let them marinate for at least 30 minutes, or up to 2 hours in the refrigerator for more flavor.
Place the marinated chicken thighs skin-side up on a baking sheet lined with parchment paper.
Pour any remaining marinade over the chicken thighs.
Bake in the preheated oven for 35-40 minutes, or until the chicken is cooked through and the skin is crispy. The internal temperature should reach 165°F (74°C).
Remove from the oven and let rest for 5 minutes. Garnish with sliced green onions and sesame seeds before serving.