Prepare the Teriyaki Sauce: In a mixing bowl, whisk together the soy sauce, brown sugar, honey or maple syrup, garlic, ginger, rice vinegar, and water or chicken broth until well combined.

Layer the Chicken: Place the chicken thighs or breasts into the slow cooker, ensuring they are evenly spaced.

Coat the Chicken with Sauce: Pour the prepared teriyaki sauce over the chicken, ensuring each piece is well-coated.

Set and Cook: Cover the slow cooker and cook on low for 4 to 6 hours until the chicken is tender and reaches an internal temperature of 165°F.

Thicken the Sauce: Remove the chicken, mix cornstarch with cold water, and stir into the remaining sauce to thicken.

Coat the Chicken Again: Return the chicken to the slow cooker and toss in the thickened sauce.

Garnish and Serve: Garnish with sliced green onions, sesame seeds, or fresh cilantro and serve with rice and vegetables.