Arrange the chicken thighs in the slow cooker and season lightly with salt and black pepper.
In a medium-sized bowl, whisk together honey, soy sauce, ketchup, minced garlic, oregano, ginger, and red pepper flakes (if using). Pour this mixture over the chicken, ensuring it’s well coated.
Cover and cook on low for 4-5 hours or on high for 2-3 hours until the chicken is fully cooked and tender.
For a thicker sauce, remove the chicken from the slow cooker and set it aside. Combine cornstarch and water in a small bowl, then whisk it into the sauce. Turn the slow cooker to high and cook the sauce for an additional 10-15 minutes until it thickens. Return the chicken to the sauce.
Serve the chicken with sauce drizzled over the top. Garnish with sesame seeds or green onions if desired.