In a large bowl, whisk together honey, soy sauce, ketchup, minced garlic, rice vinegar, ground ginger, and black pepper until well combined.
Place the chicken thighs in the slow cooker and pour the honey garlic sauce over them, ensuring the chicken is well coated.
Cover and cook on low for 6-7 hours or on high for 3-4 hours, until the chicken is tender and fully cooked.
Once cooked, remove the chicken from the slow cooker and set aside.
In a small bowl, mix cornstarch and water to create a slurry. Pour this into the sauce in the slow cooker and stir well.
Turn the slow cooker to high and let the sauce thicken for about 10-15 minutes, stirring occasionally.
Shred the chicken using two forks and return it to the slow cooker, mixing it with the thickened sauce.
Serve hot, garnished with sliced green onions and sesame seeds if desired.