To prepare the seafood, peel and devein the prawns. Cut the fish into 3 cm chunks. Gently grasp the squid body with one hand; with the other, pull the tentacles and the quill from inside the body. Wash the insides and remove the flaps and skin by pulling off. Cut the squid in half, then gently score the inside of the flesh in a crisscross pattern (without cutting through), then slice into bite-sized pieces. To use the tentacles, cut into shorter lengths.
Combine all the sauce ingredients in a bowl, ensuring that the cornflour is well blended.
Heat a wok or non-stick frying pan over a high heat. Add 1½ tablespoons of the oil and cook the fish for 1 minute, tossing frequently. Add the prawns and squid and cook for 1–2 minutes or until the prawns are almost cooked. Transfer to a plate to keep warm.
Heat the remaining oil in the wok, then toss the ginger and garlic for 30 seconds. Cook the broccoli and carrot for 1 minute, until they begin to soften but still retain their crispness. Return the seafood to the wok, add the spring onions and the sauce. Cook for 1 minute or until the sauce thickens and the seafood is perfectly cooked.