In a liquid measuring cup or small bowl, whisk together soy sauce, brown sugar, water, honey, cornstarch, ground ginger, 1/2 teaspoon garlic powder, and 1 tablespoon sesame seeds until smooth; set the teriyaki sauce aside.
Spray a large skillet with nonstick spray (or wipe with a little oil) and heat over medium; add 1 tablespoon olive oil to the pan.
Season the chicken breasts with 1 teaspoon garlic powder, salt, and pepper, then add the chicken to the hot skillet.
Cook the chicken, stirring or turning frequently, until cooked through and no longer pink in the center, about 7–10 minutes depending on thickness.
Pour the prepared teriyaki sauce over the cooked chicken and bring to a simmer; stir frequently as the sauce thickens, coating the chicken evenly.
When the sauce has thickened to your liking, remove from heat, sprinkle with extra sesame seeds, and serve with steamed broccoli and white rice if desired.
