Place the chicken breasts in the bottom of the slow cooker.
In a medium bowl, whisk together the honey, soy sauce, hoisin, olive oil, garlic, onion and crushed red pepper flakes, and then pour the sauce over the chicken.
Cover the slow cooker and cook the chicken on LOW for 4 to 5 hours until the chicken is cooked through.
Transfer the chicken to a cutting board and use two forks to shred the chicken. Place the chicken in a large bowl.
In a small bowl, whisk together the cornstarch with 3 tablespoons of cold water to make a slurry.
Transfer the liquids from the slow cooker into a small saucepan set over medium-high heat and whisk in the slurry. Bring the sauce to a boil and cook it until it reduces and has thickened slightly, about 3 minutes.
Pour the sauce over the chicken, tossing to combine. Serve the chicken topped with sliced scallions and sesame seeds.