Slice the top and bottom off the grapefruit so that they sit flat on a chopping board. Using a small serrated knife, cut off the peel and pith. Then, holding the fruit over a bowl to catch any juice (add to a citrus juice drink), cut segments between the membranes.
Thickly slice the Chinese cabbage leaves and put in a serving bowl, along with the grapefruit segments and pomegranate seeds. Scatter over the prawns and the coriander leaves.
Mix crème fraîche and lime zest and drizzle over to serve.