In a large bowl, combine the soy sauce, brown sugar, bourbon, garlic, ginger, and red pepper flakes (if using). Stir until the sugar is dissolved.
Place the chicken pieces in the Crock Pot and pour the sauce mixture over the chicken, ensuring all pieces are coated.
Cover and cook on low for 6-7 hours or on high for 3-4 hours, until the chicken is tender and cooked through.
In the last 30 minutes of cooking, mix the cornstarch and water in a small bowl to create a slurry. Stir this mixture into the Crock Pot to thicken the sauce.
Once done, serve the bourbon chicken over cooked rice and garnish with sliced green onions.