Place chicken breasts in the slow cooker.
In a bowl, whisk together garlic, ginger, honey, brown sugar, soy sauce, sesame oil, and rice vinegar.
Pour the sauce over the chicken.
Cover and cook on high for 3 hours or low for 5–6 hours.
Remove chicken and shred using two forks.
Strain the cooking liquid into a saucepan.
Bring the sauce to a simmer over medium-high heat.
Mix cornstarch with water until smooth, then add to the sauce.
Cook for 1–2 minutes until thickened.
Pour the sauce over shredded chicken and toss to coat.
Garnish with sesame seeds and green onions.
This Slow Cooker Teriyaki Chicken is best served over rice or noodles for a complete and satisfying meal.