Combine sesame oil, soy sauce, light brown sugar, orange juice, hoisin sauce, ground or rehydrated ginger and garlic in a bowl. Mix well and set to the side.
Place the chicken in a slow cooker then pour the sauce mixture over the chicken. Cover and cook on LOW for 2 1/2 hours or until chicken is tender. Transfer chicken to a platter; keep warm.
Pour cooking liquid through a sieve into a small saucepan to measure 1 1/4 cups. Discard the strained solids.
Bring the sauce to a boil over medium-high heat. Combine the cornstarch and cold water in a small bowl and mix until incorporated.
Add cornstarch mixture to sauce, stirring with a whisk until blended. Cook for 1 minute or until sauce thickens, stirring constantly.
Pour sauce over the chicken and sprinkle with sesame seeds and green onions.