Season the sliced chicken with a little salt and pepper. Heat vegetable oil in a large skillet or wok over medium-high heat. Add the chicken and cook for 5–7 minutes until browned and cooked through. Transfer the chicken to a plate.
In the same skillet, reduce heat slightly and add a touch more oil if needed. Sauté garlic and ginger for 30 seconds until fragrant.
Add the zucchini slices and stir-fry for 3–5 minutes until tender but still slightly crisp. Avoid overcooking to maintain texture.
Return the chicken to the skillet. Stir together the soy sauce, oyster sauce, rice vinegar, and sesame oil, then pour it into the pan. Toss to coat evenly. If you want a thicker sauce, stir in the cornstarch slurry and cook for another 1–2 minutes.
Remove from heat. Garnish with sesame seeds or chopped green onions if desired. Serve hot over rice, noodles, or enjoy as-is.