In a saucepan, bring the vegetable broth to a boil. Add the couscous and lemon zest, stirring to combine. Remove from heat, cover, and let it sit for 5 minutes.
Fluff the couscous with a fork once it's cooked and allow it to cool to room temperature.
In a small bowl, whisk together the lemon juice, olive oil, salt, pepper, and crushed red pepper flakes (if using) until well combined.
In a large bowl, combine the cooled couscous, diced cucumber, red bell pepper, cherry tomatoes, and red onion.
Pour the dressing over the couscous mixture and gently stir to combine.
Add the chopped parsley and mint, folding them into the salad until evenly distributed.
Taste and adjust seasoning if needed, then let the salad chill in the refrigerator for at least 30 minutes before serving to allow the flavors to meld.
Notes
Serve in a large bowl, garnished with lemon wedges and mint.