In a medium bowl, combine the boneless skinless chicken breasts with 1 tablespoon of low sodium soy sauce, 1 teaspoon of apple cider vinegar, and 1 teaspoon of granulated sugar. Mix well and set aside to marinate for about 10 minutes.

In a small bowl, whisk together the remaining soy sauce, apple cider vinegar, granulated sugar, minced fresh ginger, minced garlic, water, cornstarch, and a pinch of red pepper flakes. Set aside.

Trim the ends off the zucchini and slice it in half lengthwise, then cut each half into 1/4-inch half moons. Thinly slice the onion.

Heat 1 tablespoon of olive oil in a large skillet over medium-high heat. Add the marinated chicken and sauté for 3-4 minutes until golden brown and cooked through. Remove and set aside.

In the same skillet, heat another tablespoon of olive oil. Add sliced onions and cook for 4-5 minutes until tender and caramelized.

Pour the sauce into the skillet with onions, stirring well. Once it begins to bubble, add the zucchini and cook for another 3 minutes until just tender.

Return the cooked chicken to the skillet, tossing everything together until well mixed and heated through. Garnish with sesame seeds and chopped green onion before serving.