Bring a large saucepan of salted water to the boil and blanche the cabbage leaves for 30 seconds until soft. Drain and refresh the leaves in iced water. Bring a large saucepan of water to a gentle simmer. Rub the salmon fillets with the olive oil, then season and cover all over with a thin layer of the roughly chopped coriander leaves. Wrap the blanched cabbage leaves around the salmon and coriander so that they are completely enveloped in cabbage.
Place the wrapped salmon fillets in a large double boiler and steam over the saucepan of simmering water for 10-12 minutes until the fish feels firm to the touch. Remove and transfer to wooden serving boards or plates. Cut through and garnish with sprigs of coriander before serving.