Toss the tomatoes, lemon juice & 1 tsp. salt in a bowl & set aside.
Put the couscous in a large bowl. Bring the water, lemon zest, 3 tbsp. olive oil, 1 tsp. salt, cayenne & herb stems to a boil over high heat. Pour the liquid over the couscous & stir to separate any clumps. Cover with a lid or plate and set aside for 5 minutes. Remove the zest & herb stems and fluff with a fork.
Add the tomatoes, scallions, mint, parsley & pine nuts. Drizzle the remaining olive oil over the salad, toss & serve.
Serves 6-8