Place the chicken thighs or breasts in the bottom of a 6‑quart crockpot in a single layer.
In a bowl, whisk together soy sauce, brown sugar, honey, rice vinegar, minced garlic, grated ginger, and sesame oil until smooth.
Pour the teriyaki sauce evenly over the chicken, turning pieces to coat.
Cover the crockpot and cook on LOW for 5–6 hours or on HIGH for 3–4 hours, until chicken is very tender.
When chicken is done, remove pieces to a cutting board and shred with two forks or chop to desired size.
Pour the crockpot liquid into a saucepan or keep in the crockpot on HIGH for thickening.
Mix 2 tbsp cornstarch with 2 tbsp cold water to make a slurry.
Bring the sauce to a simmer and whisk in the slurry; cook until thickened, about 2–3 minutes.
Return shredded chicken to the thickened sauce and stir to coat thoroughly.
Taste and adjust seasoning—add a splash of rice vinegar for brightness or a pinch of red pepper flakes for heat.
Garnish with sliced green onions and sesame seeds before serving over steamed rice, noodles, or vegetables.