Preheat oven to 425˚F.
Grease a baking dish with cooking spray and set aside.
Pound the chicken breasts to an even thickness, but do not pound them thin.
Arrange the chicken breasts on the bottom of the baking dish.
Add sliced onions over the chicken and set aside.
In a mixing bowl, combine honey, soy sauce, rice vinegar, garlic, and ginger; whisk until thoroughly combined.
Pour the sauce mixture over the chicken; make sure that the chicken is nestled down in the sauce.
Bake for 30 minutes, or until the internal temperature of the chicken reaches 165˚F degrees.
Remove from oven and transfer the chicken and cooked onions to a serving platter. Set aside.
Transfer the remaining teriyaki sauce from the baking dish to a frying pan or a saucepan set over medium-high heat.
In a separate bowl, whisk together the cold water and cornstarch until the cornstarch is completely dissolved.
Pour the cornstarch mixture into the teriyaki sauce and whisk to combine.
Bring the mixture to a boil and let boil for about 1 to 2 minutes or until thickened.
Remove from heat and spoon the sauce over the chicken.
Garnish with sesame seeds and chopped green onions.
Serve over rice.