Place the chicken thighs in an even layer at the bottom of the slow cooker.
Whisk honey, soy sauce, ketchup, vegetable oil, garlic, onion, and oregano in a mixing bowl until combined.
Pour the sauce mixture over the chicken thighs.
Cover and cook on high for 3 to 4 hours (or on low for 6 to 7 hours).
Remove the chicken from the slow cooker and transfer to a cutting board to shred or chop into bite-sized pieces.
In a small container, whisk cornstarch and cold water until smooth to form a slurry.
Stir the slurry into the liquid remaining in the slow cooker. Cover and cook on high for an additional 15 minutes until the sauce thickens.
Return the chicken to the slow cooker and toss thoroughly to coat with the thickened sauce.
Serve warm over rice, garnished with sesame seeds and green onions.