In a large bowl, combine the soy sauce, brown sugar, bourbon, ketchup, apple cider vinegar, garlic, ginger, and red pepper flakes. Whisk until well blended.
Place the chicken pieces in the slow cooker and pour the sauce mixture over the chicken. Stir to coat the chicken evenly.
Cover and cook on low for 4 to 6 hours or on high for 2 to 3 hours, until the chicken is cooked through and tender.
Once the chicken is cooked, mix the cornstarch and water in a small bowl to create a slurry. Stir the slurry into the slow cooker and cook on high for an additional 15-30 minutes, until the sauce thickens.
Serve the bourbon chicken over cooked rice and garnish with sliced green onions.