Cook the Couscous: In a medium saucepan, bring the vegetable broth or water to a boil. Stir in the couscous, cover, and remove from heat. Let it sit for 5 minutes, then fluff with a fork.
Prepare the Salad: In a large mixing bowl, combine the cooked couscous, diced cucumber, cherry tomatoes, red onion, chopped parsley, chopped mint, and crumbled feta cheese.
Make the Dressing: In a small bowl, whisk together the extra-virgin olive oil, fresh lemon juice, lemon zest, za'atar seasoning (if using), salt, and pepper.
Toss and Serve: Pour the dressing over the salad and toss until well combined. Taste and adjust seasoning if necessary. Serve the salad immediately or refrigerate for later.