In a medium bowl, whisk together light soy sauce, rice vinegar, sesame oil, and corn starch until smooth. Slice the chicken breast and add to the bowl, ensuring coated. Marinate in the refrigerator for 20–30 minutes.

While chicken marinates, combine water, light soy sauce, oyster sauce, rice vinegar, brown sugar, and additional corn starch in another bowl. Stir well and set aside.

Heat oil in a skillet over high heat. Add marinated chicken in a single layer; cook for 4–5 minutes, browning on one side before flipping. Remove from skillet.

In the same skillet, add more oil if needed, then toss in sliced mushrooms and zucchini. Stir-fry for 2–3 minutes until crisp-tender.

Lower heat to medium. Return the seared chicken to the skillet with vegetables. Add minced garlic and grated ginger; stir-fry for about 1 minute.

Pour the prepared sauce over chicken and vegetables, stirring to coat. Increase heat slightly, cooking until the sauce thickens and bubbles, about 2–3 minutes. Serve immediately over rice or noodles.