In a large bowl, whisk together all of the sauce ingredients until the cornstarch is fully dissolved.
Add the chicken to the bottom of your slow cooker, then layer in the chopped vegetables, onion, and pineapple chunks. Pour the sauce over the top and gently stir to coat everything evenly.
Cover and cook on High for about 2½ hours, or until the chicken is fully cooked and tender.
About 30 minutes before the chicken is finished, prepare the coconut rice. In a medium saucepan, combine the coconut milk, coconut water, a pinch of salt, and the rinsed rice. Stir, bring to a boil, then cover, reduce the heat to low, and simmer according to your rice package directions, about 15-20 minutes.
Once the chicken is cooked, shred or slice it if desired, then stir everything together so the chicken and vegetables are coated in the sauce.
Divide the coconut rice between bowls, then top with the chicken and vegetables. Spoon some of the extra sauce from the slow cooker over the top and garnish with fresh cilantro and additional pineapple, if desired.