In a small bowl, whisk together all sauce ingredients until combined.
Lay chicken thighs in the bottom of a slow cooker and pour sauce evenly over top.
Place the lid on the slow cooker and cook on LOW for 6-7 hours or HIGH for 3-4 hours.
Transfer cooked chicken thighs to a cutting board and cut into 1-inch pieces.
In a small bowl, whisk together 3 tbsp. water with cornstarch until smooth.
Place slow cooker on HIGH heat and whisk in the cornstarch mixture.
Place the lid back on the slow cooker and cook for about 10 minutes, stirring occasionally, until sauce thickens.
Add chicken and scallions to the thickened sauce and stir to coat.
Serve hot over rice or noodles.