Place chicken thighs in a slow cooker (5 to 7 quart).
In a mixing bowl whisk together ketchup, honey, soy sauce, sriracha, sesame oil, garlic and ginger. Pour mixture evenly over chicken thighs in slow cooker.
Cover and cook on low heat until cooked through and tender, about 3 to 4 hours (should register 165 °F in center).
Transfer chicken to a serving plate, cover with foil to keep warm.
Pour juices from slow cooker into a medium saucepan (you should have 2 cups liquid), add vinegar. Heat over medium heat and bring to a simmer.
Meanwhile in a small mixing bowl whisk together cornstarch with 2 Tbsp water until well blended. Pour mixture into sauce in skillet.
Simmer sauce, whisking constantly for 1 minute.
Pour sauce over chicken (or baste over chicken) and garnish with green onions and sesame seeds if desired.