Pat prawns dry with a paper towel. Toss with cornflour, salt, and white pepper. Set aside.
Cook the noodles
Cook noodles for 2 minutes less than the packet instructions.
Mix the sauce
In a small bowl, whisk together oyster sauce, light soy, dark soy, fish sauce, sugar, and lime juice.
Sear the prawns
Heat a wok or large pan over high heat until just smoking. Add a splash of neutral oil, then stir-fry prawns for 90 seconds–2 minutes until just pink and lightly charred. Remove and set aside.
Stir fry aromatics
In the same wok, add garlic and chilli, frying for 20–30 seconds until fragrant.
Add vegetables
Toss in carrot, onion, green beans, and cabbage. Stir fry 2–3 minutes until bright and just tender.
Combine
Add the cooked noodles and sauce. Toss vigorously over high heat until noodles are glossy and coated. Return prawns to the wok along with bean sprouts, spring onions, and Thai basil. Toss through for 30 seconds to finish.
Serve
Divide into containers or serve immediately with lime wedges and optional peanuts.