Place the chicken thighs in the slow cooker.
In a medium bowl, combine the pineapple chunks, soy sauce, brown sugar, ketchup, minced garlic, minced ginger, black pepper, and red pepper flakes. Mix well.
Pour the sauce mixture over the chicken in the slow cooker, ensuring the chicken is well coated.
Cover and cook on low for 6-8 hours or on high for 3-4 hours, until the chicken is tender and fully cooked.
Once cooked, shred the chicken using two forks and stir it back into the sauce.
Serve the chicken over rice or with your favorite sides, garnished with chopped green onions and sesame seeds if desired.