Bring a large pot of water to a rolling boil and cook the chow mein noodles according to package directions until just tender. Drain immediately and rinse briefly with cold water to stop the cooking. Toss lightly with a few drops of oil to prevent sticking and set aside.
In a small bowl, whisk together the soy sauce, oyster-style sauce, sugar, white pepper, water, and cornstarch until completely smooth. Set the sauce aside so it’s ready to go.
Heat a large wok or wide skillet over medium-high heat. Add the oil and let it heat until shimmering but not smoking.
Add the sliced onions and stir-fry for about 1 minute, just until they begin to soften and turn translucent.
Stir in the garlic and cook for 10–15 seconds, keeping it moving so it becomes fragrant without browning.
Add the cabbage and celery to the pan. Stir-fry for 1–2 minutes, allowing the vegetables to soften slightly while still keeping a bit of crunch.
Add the cooked noodles to the wok, spreading them out gently over the vegetables.
Pour the prepared sauce evenly over the noodles. Using tongs or two spatulas, toss everything together continuously for 2–3 minutes until the sauce thickens and coats every strand of noodle.
Taste and adjust seasoning if needed, then remove from heat immediately to avoid overcooking.
