In a medium bowl, add the tomatoes, cucumbers, lemon juice, and 2 teaspoons salt, then toss to combine.
In a medium saucepan, add the water, lemon zest, oil, 1 teaspoon salt and cayenne pepper and bring to a boil over high heat. Once boiling, remove from heat and add the couscous, stirring well and then covering for 5 minutes.
Fluff the couscous with a fork, then transfer to a serving bowl. Add the tomato mixture and the scallions and toss to combine.