Use a 7-8cm ring mould or a plastic half-litre drinking bottle cut into rings.
In a mixing bowl, mix together the freshly grated ginger, the lime juice and the lime zest, then the peeled, deseeded and diced cucumber, the finely chopped coriander and the skinned, diced salmon fillet. Season to taste with salt and freshly ground black pepper and, when mixing, be careful not to break up the fish too much.
Place the ring in the centre of a plate and fill with some of the mixture to a depth of about 2-3cm. Repeat with the remaining portions then serve.