Bring the orange juice, vinegar and ginger to the boil, reduce to half the amount. Put the reduction to one side. Heat the oil, sauté the onion, add the lentils and continue to cook. Pour in the stock and bring to the boil. Cover and simmer over a medium heat for approx. 40 mins. Add the tomatoes, season.
Heat the oil in a non-stick frying pan. Fry the salmon fillets for approx. 3 mins. on each side, season.