Prep your chicken. Add it to a large skillet along with the olive oil. Stir until chicken is coated. Cook over medium-high heat, stirring often, for 5-7 minutes, or until it's cooked through (don't overcook).
Meanwhile, spiralize your zucchini and set aside. Add the teriyaki sauce ingredients to a small bowl and whisk together. Also get your cornstarch mixture ready in another small bowl and chop the scallions if using.
When the chicken is about done, reduce the heat to medium and add the teriyaki sauce mixture and the cornstarch mixture to the skillet. Stir well so the chicken is coated, and let it bubble (it will thicken fast) for a minute or two.
Add the zucchini noodles to the skillet and using tongs, toss them with the teriyaki chicken. The zucchini will release water. Don't cook the zoodles for too long or they will get limp and watery. I warm them through for a couple of minutes max, tossing continuously.
Serve immediately with scallions sprinkled over top if desired. Enjoy!