Place the prawns in a glass or ceramic bowl and add all the ingredients for the marinade. Toss to coat evenly, cover and leave to marinate at room temperature for 10 minutes.
Meanwhile, spray a large nonstick wok or frying pan with cooking spray and heat over a high heat. Add the onion and stir-fry for about 3–4 minutes until softened. Add the broccoli, carrot, spring onions and ginger and stir-fry for about 3–4 minutes until just tender. Stir in the stock and cook for 2–3 minutes.
Stir the prawn mixture and oyster sauce into the pan and cook, stirring, for about 3–4 minutes until the prawns have turned pink and are firm. Serve with rice or noodles.