Make the marinade: In a bowl, combine tamari, honey, rice vinegar, sesame oil, garlic, ginger, black pepper, and chili flakes.

Marinate the chicken: Add the chicken thighs and toss until well coated. Let them marinate for at least 15 minutes, or refrigerate for up to 4 hours for deeper flavor.

Sear the chicken: Heat vegetable oil in a large skillet over medium-high heat. Add the chicken thighs in a single layer and cook for 5–6 minutes on each side until golden brown.

Add the sauce: Pour the remaining marinade into the skillet. Reduce the heat to medium-low and cook for 5–7 minutes, turning the chicken occasionally, until the sauce becomes glossy and the chicken is fully cooked.

Check doneness: The thickest part of the chicken should reach 74°C (165°F).

Garnish: Remove from the heat and sprinkle with sliced green onions and sesame seeds.

Serve: Serve hot with steamed rice, stir-fried vegetables, or a fresh cucumber salad.