Spray your slow cooker with cooking spray and place the chicken breasts in the bottom. In a small bowl whisk the soy sauce, honey, rice wine vinegar, onion, garlic, pepper and ginger. Pour over the chicken breasts.
Cook on high for 3-4 hours or low for 4-5 or until chicken is cooked throughout and shreds easily. Once the chicken is cooked, remove with a slotted spoon and shred on a plate.
Pour the sauce into a medium sauce pan. In a small bowl, whisk together the water and cornstarch. Slowly whisk into the sauce on medium high heat. Continue to whisk and let it boil until the honey teriyaki sauce starts to thicken. About 2 minutes.
Add the chicken back to the slow cooker and pour the sauce on top stirring to coat. Serve over rice and garnish if desired.