Cook noodles according to package instructions; drain and set aside.

In a large skillet or wok, heat vegetable oil over medium-high heat.

Season chicken breasts with salt and pepper, and add to the skillet. Cook until browned and cooked through, about 5-7 minutes, then remove from the skillet and slice.

In the same skillet, add cabbage, carrot, celery, and the white parts of the green onions. Stir-fry for 2-3 minutes until vegetables are tender.

Add garlic and ginger, cooking for an additional 30 seconds until fragrant.

In a bowl, mix together oyster sauce, soy sauce, sesame oil, rice vinegar, cornstarch, and brown sugar. Pour sauce into the skillet and stir to combine.

Return chicken to the skillet, add cooked noodles, and toss to coat all ingredients evenly. Cook for another 2-3 minutes until heated through.

Serve immediately, garnished with the green parts of the green onions and bean sprouts if using.