In a small bowl, whisk together the soy sauce, sesame oil, sugar, rice vinegar, grated ginger, cornstarch, and oyster sauce until the cornstarch is fully dissolved and the mixture is smooth. This creates a velvety sauce base and helps the cornstarch coat the chicken evenly. Add the chicken thigh chunks to the marinade and stir to coat completely. Let the chicken marinate for at least 30 minutes at room temperature—this allows the flavors to penetrate the meat and the cornstarch to create a silky coating when cooked.

While the chicken marinates, mince the garlic cloves and slice the zucchini into 1/4-inch thick half-moons. Having everything prepped and ready before you start cooking is essential for stir-frying—the cooking happens fast and there's no time to chop once the heat is on. Set both ingredients aside in separate small bowls or on a cutting board.

Heat the avocado oil in a large skillet or wok over medium-high heat until it shimmers—you should see a slight haze above the pan. I prefer avocado oil here because it has a high smoke point and won't burn at the temperature needed for proper browning. Working quickly, add the marinated chicken (including all the marinade) and cook for about 2 minutes, stirring frequently, until the chicken is lightly browned on the outside. The chicken doesn't need to be cooked through at this point—it will finish cooking in the final step. Transfer the chicken to a clean plate using a slotted spoon, leaving as much of the sauce as possible in the pan.

Add the minced garlic to the same pan and cook for about 30 seconds, stirring constantly, until fragrant—this quick burst of heat releases the garlic's aromatic oils. Immediately add the zucchini slices and stir-fry for about 5 minutes, stirring frequently, until they're tender-crisp and beginning to soften. The zucchini should still have a slight bite to it—avoid overcooking or it will become mushy and lose its texture.

Return the cooked chicken to the pan along with all accumulated juices from the plate. Stir everything together and cook for 2-3 minutes more, until the chicken is cooked through and the sauce thickens slightly from the cornstarch. Season with black pepper to taste. The dish is ready to serve immediately while everything is hot and the zucchini maintains its tender-crisp texture.