Put all of the couscous into a large bowl. Then boil the vegetable stock and pour over the couscous. Now cover with cling film and leave to set.
Heat the oil in a frying pan on a low heat for a minute or 2. Then add the onion and cook until translucent.
Season with salt and pepper to taste and then simmer gently without stirring. Add a little water if the mixture starts to dry out.
Using a fork, fluff the couscous before adding the remaining tomato and the diced cucumber. Now add the onion and herb mixture.
Take your lemon half and squeeze generously over the mixture. Eat it now, or chill it until you’re ready.