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 place the chicken in the skillet.
Cook the chicken for about 6-7 minutes on each side, or until the internal temperature reaches 165°F and the chicken is nicely browned.
Remove the chicken from the skillet and let it rest for a few minutes. Slice the chicken into strips.
Serve the chicken warm, garnished with chopped green onions and sesame seeds if desired.