1) Toss the tomatoes, cucumbers, and lemon juice in a bowl with 2 tsp of the salt. Set aside.
2) Put the couscous into a large bowl. Bring the water, lemon zest, 3 tbsp of the oil, the remaining salt, cayenne, and herb stems to a boil over high heat. Pour the liquid over the couscous, stir to separate any clumps. Cover with a lid, plate, or clingfilm, set aside for 5 mins. Remove the zest and herb stems and fluff with a fork.
3) Add the tomato mixture, spring onions, mint, parsley, and pine nuts. Drizzle the remaining oil over the salad, toss and serve.