In a large bowl, combine soy sauce, brown sugar, bourbon, ketchup, minced garlic, minced ginger, and crushed red pepper flakes (if using). Whisk until well blended.
Place the chicken pieces in the crock pot and pour the sauce mixture over the chicken, stirring to coat evenly.
Cover the crock pot and cook on low for 6-7 hours or on high for 3-4 hours, until the chicken is cooked through and tender.
In a small bowl, mix cornstarch and water to create a slurry. About 30 minutes before serving, stir the slurry into the crock pot to thicken the sauce.
Once the sauce has thickened, serve the bourbon chicken over cooked rice and garnish with chopped green onions.