Place the chicken thighs in the bottom of the Crock Pot.
In a medium bowl, whisk together the soy sauce, brown sugar, bourbon, ketchup, minced garlic, ground ginger, and red pepper flakes (if using).
Pour the sauce mixture over the chicken in the Crock Pot, ensuring the chicken is well coated.
Cover and cook on low for 6 to 7 hours or on high for 3 to 4 hours, until the chicken is tender and cooked through.
Once cooked, remove the chicken from the Crock Pot and shred it using two forks.
In a small bowl, mix the cornstarch and water to create a slurry. Stir this mixture into the sauce in the Crock Pot and cook on high for an additional 15 minutes, or until the sauce thickens.
Return the shredded chicken to the Crock Pot, stirring to combine with the thickened sauce.
Serve the bourbon chicken over cooked rice and garnish with chopped green onions.