Place the chicken pieces in a bowl. Add the cornstarch and salt and pepper. Toss to coat the chicken in the cornstarch mixture.
Heat the oil in a large pan over medium high heat. Add the chicken in a single layer and cook for 3-4 minutes on each side until browned. You may need to work in batches.
Coat a slow cooker with cooking spray and add the chicken to the slow cooker.
In a small bowl, whisk together the orange marmalade, soy sauce, rice vinegar, sesame oil and garlic.
Pour the sauce over the chicken and gently stir to coat.
Cook on LOW for 2-3 hours.
Sprinkle with sesame seeds and green onions, then serve.
