Arrange chicken thighs evenly in the slow cooker insert.
In a mixing bowl, combine soy sauce, honey, ketchup, minced garlic, apple cider vinegar, grated ginger and red pepper flakes, stirring until well mixed.
Pour the prepared sauce evenly over the chicken in the slow cooker.
Cook on high for 3.5 hours or on low for 6 to 8 hours until the chicken is well cooked and tender.
Whisk cornstarch with 2 tablespoons cold water until smooth.
Add the cornstarch mixture into the slow cooker and stir to incorporate.
Continue cooking on high for an additional 15 minutes to thicken the sauce.
Serve the chicken whole or shred it using two forks directly in the slow cooker.
Optionally, serve over rice garnished with scallions and sesame seeds for extra flavor and texture.