Place chicken in Crock Pot and season both sides with pepper.
In a medium bowl, combine onion, garlic, honey, ketchup, soy sauce, oil and red pepper flakes. Pour over chicken. Cook on low for 4 hours, or high for 3 hours.
Remove chicken to a cutting board. Shred chicken into bite-sized pieces; set aside.
In a small bowl, dissolve 4 teaspoons cornstarch in 1/3 cup water; add to crock pot. Stir to combine with sauce. Cover and cook sauce on high for ten more minutes, stirring often, until slightly thickened.
Add Chicken back into sauce and heat through. Serve over rice and top with scallions and sesame seeds.