Prepare the noodles according to package instructions until just shy of al dente. Drain and rinse with cold water to stop cooking and keep them from sticking.
While the noodles cook, slice the chicken into thin, bite-sized strips. If you’re using any thick pieces, you can pound them slightly to even thickness for quicker, uniform cooking.
In a small bowl, whisk together the soy sauce, oyster sauce, rice vinegar, white pepper (if using), cornstarch, and water or broth. This will be your stir-fry sauce that glazes the noodles.
Heat a large skillet or wok over medium-high heat. Add 1 teaspoon of oil and sear the chicken in a single layer until it’s just cooked through, about 2–3 minutes per side depending on thickness. Remove the chicken and set aside.
In the same pan, add another teaspoon of oil. Stir-fry the garlic for about 15 seconds until fragrant, then add the bell pepper, carrot, and other vegetables. Cook for 2–4 minutes until they’re crisp-tender.
Return the chicken to the pan. Pour the prepared sauce over the chicken and vegetables, stirring to coat everything evenly. Let the sauce simmer for about 1–2 minutes until it slightly thickens.
Add the cooked noodles to the pan and toss gently to coat with the sauce. If the mixture seems dry, splash in a little more water or broth and keep tossing until the noodles are glossy and heated through.
Taste and adjust to your preference. A splash more soy for salt, a pinch more vinegar for brightness, or a touch more cornstarch slurry if you like it heftier.