In a large saucepan of salted boiling water cook noodles for 3–5 minutes, until al dente. Drain and set aside.
Heat oil in a wok or large nonstick skillet. Add cabbage, pepper, garlic, ginger and orange zest and cook for about 1 minute. Add chicken stock and cook for 2–3 minutes, until vegetables are tender-crisp.
Add Udon noodles and reserved sauce and cook for 1 minute, or until heated through, about 2 minutes.
Add green onions and bean sprouts and stir to combine. Transfer to a platter and sprinkle with deep fried noodles.
Tip: Broad egg noodles can be substituted.
In a bowl, combine plum sauce, soy sauce, mirin, fish sauce and sesame oil. Set aside.