01 - In a large bowl, whisk together miso paste, soy sauce, mirin, honey, sesame oil, garlic, ginger, rice vinegar, and black pepper until smooth and well combined.
02 - Add chicken thighs to the marinade, turning to coat thoroughly. Cover and refrigerate for at least 30 minutes (up to 4 hours for deeper flavor development).
03 - Preheat oven to 400°F. Line a baking tray with parchment paper or foil for easy cleanup.
04 - Remove chicken from marinade and arrange on the prepared baking tray, shaking off excess marinade to prevent burning.
05 - Roast for 25 to 30 minutes, or until chicken is cooked through and edges are caramelized and lightly browned.
06 - Transfer to a serving platter. Sprinkle with toasted sesame seeds and sliced spring onions if desired. Serve hot with steamed rice and vegetables.