In a large bowl, combine the soy sauce, honey, rice vinegar, minced ginger, minced garlic, red pepper flakes, and black pepper. Whisk until well blended.
Add the chicken thighs to the marinade, ensuring they are fully coated. Cover and refrigerate for at least 30 minutes, or up to 2 hours for more flavor.
Heat the vegetable oil in a large skillet over medium-high heat. Remove the chicken from the marinade, allowing excess marinade to drip off, and add the chicken to the skillet.
Cook the chicken for about 5-7 minutes on each side, or until the chicken is cooked through and has a nice caramelized color.
Remove the chicken from the skillet and let it rest for a few minutes before slicing.
Serve the chicken sliced, garnished with chopped green onions and sesame seeds if desired.