If using packaged yakisoba noodles, remove them from their package and microwave for 1 minute to loosen them up. If using dried noodles, cook according to package instructions, then drain and set aside.
In a small bowl, combine soy sauce, oyster sauce, sugar, sesame oil, and optional white pepper. Set aside.
Heat the vegetable oil in a large skillet or wok over medium-high heat. Add the onion and celery, cooking for 2–3 minutes until just starting to soften. Add cabbage and garlic, and cook another 2–3 minutes until wilted and slightly caramelized.
Add the noodles to the pan along with the sauce. Toss everything together using tongs until well combined and heated through, about 2–3 minutes. Let the noodles sit for a few seconds undisturbed between tossing to allow slight browning.
Serve immediately as a side or base for your favorite Panda-style protein.