Cut the chicken into approximately 1" pieces.
Pour the cornstarch into a shallow dish, add the chicken, and toss to evenly coat.
Heat the oil in a large skillet over medium high heat and add the coated chicken. Lightly brown on each side, not cooking thoroughly.
Transfer the browned chicken into the basin of a 6 quart slow cooker.
In a medium bowl, whisk together the marmalade, soy sauce, vinegar, sesame oil, ginger, garlic, red pepper flakes and sesame seeds.
Pour the sauce over the chicken.
Stir everything to combine.
Cover and cook on LOW for 2-3 hours. Check and stir halfway through to make sure it isn't burning.
Garnish with chopped scallions and a sprinkle of sesame seeds.
Serve over rice.