Place couscous in a medium heatproof bowl. Pour 1 cup boiling water over the couscous, cover, and let stand 10 minutes. Fluff with a fork.
Cut bell pepper into 1-inch-long matchsticks, and add to the warm couscous. Thinly slice the scallions crosswise, and add to the bowl. Add cherry tomatoes.
In a small bowl, whisk olive oil and lemon juice together. Season with salt and pepper. Drizzle over couscous, vegetables, and toss. Garnish with lemon zest, if desired, and serve.