Cut chicken breasts into 1 inch cubes and place inside a large ziplock bag. Set aside.
Mix together 3 tablespoons soy sauce, 1 tablespoon water, 1 tablespoon sugar, and 1 tablespoon rice wine vinegar.
Add marinade to ziplock bag and coat chicken completely. Refrigerate for 30 minutes.
Meanwhile, mix 4 teaspoons cornstarch with 2 tablespoons water and set aside.
In small saucepan mix together 3/4 cup soy sauce, 3/4 cup water, 1 tablespoon rice wine vinegar, sugar, garlic powder, and ground ginger.
Use a whisk to mix together the ingredients and then bring to a boil. Reduce heat to low.
Add cornstarch mixture into the saucepan and stir constantly until fully combined and thickened.
Heat chicken in a large skillet over medium high heat.
Pour the teriyaki sauce over all the chicken (reserving some sauce for serving) and cook until chicken is fully cooked, about 3-4 minutes on each side; depending on the thickness of the chicken.
Sprinkle the chicken with sesame seeds.
Serve over rice or with your favorite veggies, with extra teriyaki sauce on the side.