Add chicken, cornstarch, salt and pepper to a large ziplock bag. Toss to coat the chicken.
Heat oil to a large skillet or wok over medium high heat.Add in chicken in two batches and cook until golden brown on both sides, about 3-4 minutes.Add in garlic and ginger and cook for an additional minute. Transfer the chicken and garlic mixture to the slow cooker.
Meanwhile mix the sauce ingredients in a small bowl.
Add the sauce ingredients to the skillet the chicken was cooked in and bring to a simmer. Cook for 1-2 minutes making sure to scrap the brown bits (fond) off the bottom of the skillet.
Add the sauce to the slow cooker and toss to coat the chicken.Cook on low for 2-3 hours. (Mine took 2 hours exactly)
In a small bowl combine 1 tsp of cornstarch with 1 tbsp of the cooking liquid from the slow cooker. Add to the slow cooker and stir to combine. Cover and all the chicken to cook for an additional 5 minutes.Serve immediately with sesame seeds for garlic, if desired.