Mix all sauce ingredients in a small bowl and set aside.
Place chicken and cornstarch into a plastic or ziploc bag, seal bag, and shake until all pieces of chicken are coated with cornstarch.
In a large skillet heat cooking oil over medium high heat. Add in chicken in single layer and season with salt & pepper. Cook on one side until browned and flip over to cook on other side until nice and golden brown. (The chicken does not have to be cooked all the way through, it will finish cooking in the crockpot.)
In crockpot place chopped bell peppers, onions, pineapple and juice, browned chicken, and the sauce. Stir well to combine.
Place lid on crockpot and cook on low for 3-4 hours until chicken is cooked through and the vegetables are tender. Serve over white rice or fried rice. (search my blog for homemade fried rice recipe if needed.)
Garnish with green onions and sesame seeds, if desired.