Put the couscous in a shallow bowl. Add a pinch of salt to the boiling water, and pour this over the couscous to cover. Cover the bowl and set aside for 15 minutes so the couscous soaks up the liquid. Uncover, fluff up the couscous with a fork, then set aside to cool down.
Transfer the cool couscous to a mixing bowl, add the chickpeas, lentils, and cranberries, and toss. Add green onion, herbs, lemon zest, garlic, and lemon juice. Stir gently to combine, then stir in olive oil and season to taste.