Add chicken breasts to the bottom of your slow cooker in a single layer.

In a separate bowl, whisk together garlic, onion,honey, soy sauce, rice wine vinegar, ginger, and black pepper until combined.

Pour mixture on top of chicken breasts. Cover slow cooker, and cook on high 4-5 hours, or until the chiclen is cooked through and shreds easily with a fork.

Remove the chicken with a slotted spoon to a separate bowl and shred it using two forks.

Transfer the remaining teriyaki sauce from the slow cooker to a medium saucepan.

Meanwhile in a separate bo whisk together the cold water and cornstarch until the cornstarch is dissolved and no longer lumpy.

Pour the cornstarch slurry into the teriyaki sauce mixture, and whisk to combine. Bring the mixture to boil for about 1-2 minutes or until thickened. Remove from heat, and pour the sauce on top of the shredded chicken. Toss to combine.

Serve topped with scallions (green onions) and toasted sesame seeds if desired.