In a large bowl, combine hoisin sauce, soy sauce, rice vinegar, honey, sesame oil, minced garlic, grated ginger, 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 vegetable oil in a large skillet over medium-high heat. Remove chicken from the marinade, allowing excess to drip off, and place 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.
Pour the remaining marinade into the skillet and bring to a simmer. Cook for an additional 2-3 minutes, allowing the sauce to thicken slightly.
Remove from heat and let the chicken rest for a few minutes before slicing.
Serve the chicken garnished with sliced green onions and sesame seeds.