Add the chicken thighs to your slow cooker.
In a separate bowl, combine soy sauce, honey, ketchup, minced garlic, fresh ginger, sesame oil, and crushed red pepper flakes if using; whisk until mixed.
Pour this sauce evenly over the chicken in the slow cooker.
Cover and cook on low heat for between 3 to 5 hours, or on high heat for 2 to 3 hours, until the chicken is tender and cooked through to 165°F internal temperature.
Avoid lifting the lid during cooking to keep the chicken moist and tender.
Take the chicken out and shred it using two forks.
Blend the water and cornstarch together in a small dish to create a slurry.
Add the shredded chicken and cornstarch mixture back into the slow cooker sauce and stir well.
Put the lid back on and continue cooking on high for another 15 to 20 minutes until the sauce thickens.
Serve the chicken over rice, noodles, or vegetables with some sauce spooned over the top.
Garnish with sesame seeds and sliced green onions if you like.