Pour the stock into a large pan, cover and bring to the boil. Add the beans and cook, covered, for 2-3min until they are just tender. Remove with a slotted spoon and keep warm.
Put the salmon into the same pan. Cover and simmer gently for 5min until it just begins to flake. Remove with a slotted spoon and keep warm.
Put the couscous into a large bowl and pour the stock over. Cover the bowl with clingfilm and leave to stand for 5min.
Fluff up the couscous gently with a fork, stir in the green beans and tip on to a serving dish. Lay the salmon on top of the couscous and garnish with the parsley. Serve hot or at room temperature.