Place the couscous in a large pan bowl with a good pinch of salt, cover with boiling water from the kettle. Bring to the boil, and then simmer for 5 mins until the couscous is tender. Drain in a sieve and rinse well under cold water. Place in a large bowl.
Remove any tough stalks from the herbs and finely chop the leaves. Add to the couscous with the cucumber, tomatoes, oil and lemon, mix well and season to taste.