In a wok or deep skillet over medium-high heat, heat 2 tablespoons of cooking oil, then add the par-cooked noodles. Cook for 1-2 minutes, allowing the noodles to crisp, then flip and cook for another 1-2 minutes. Transfer to a plate and set aside.
In the same wok, heat the remaining tablespoon of cooking oil over medium-high heat and add the onion, bell pepper, broccoli, and carrot. Stir and cook for 2 minutes, then add the garlic and season with salt and pepper. Stir and continue to cook for 2 minutes, or until the onions are translucent.
Add the cabbage, shiitake mushrooms, snow peas, and corn.
In a small bowl, combine the water and cornstarch. Mix with a fork to dissolve the cornstarch, then add the soy sauce, hoisin sauce, rice wine, sugar, and white pepper. Mix well.
Pour the sauce over the vegetables. Mix well and cook for 3-5 minutes, or until the vegetables have softened.
Add the crispy noodles to the wok, mix well and add bean sprouts. Toss gently and cook for another 2-3 minutes, or until everything is well-combined. Garnish with sliced scallions.