In a medium mixing bowl, whisk together soy sauce, honey, peanut butter, rice vinegar, fresh ginger, minced garlic, ground cumin, and optional red pepper flakes until smooth.

Place chicken thighs in a bowl or resealable bag and pour marinade over, ensuring all pieces are well-coated. Refrigerate for at least 2 hours, ideally overnight.

Preheat grill to medium-high heat or oven to 400°F (200°C). Prepare grill grates or line baking sheet with foil.

For grilling, cook chicken thighs on grill for 6-8 minutes each side. For roasting, bake for 35-40 minutes, basting occasionally.

As chicken finishes cooking, chop cilantro and toast sesame seeds in skillet over medium heat for 2-3 minutes.

Transfer chicken to serving platter, sprinkle with cilantro and sesame seeds, and serve hot.