To make the dressing, in a small mixing bowl, whisk together the lemon zest and juice, garlic, 1/2 cup olive oil, 2 teaspoons of salt and 1 teaspoon of pepper. Set the dressing aside.
To make the salad, combine the bell pepper, cucumber, onion, chickpeas, olives, walnuts, mint and parsley in a large mixing bowl.
Meanwhile, bring a large pot of water to a boil. Stir in 3 tablespoons of salt and a small splash of olive oil. Add the orzo and cook for 7 to 9 minutes, or according to the directions on the package. Drain the orzo in a colander, then add it to the vegetable mixture while the orzo is still hot. Immediately pour the dressing onto the orzo and vegetables, and stir to combine. The hot orzo will readily absorb the dressing. Add a splash more olive oil if the salad seems too dry. Allow the salad to cool to room temperature, and add the feta, if desired. Cover and refrigerate for 1 to 2 hours.
Give the salad a stir, then taste and adjust the seasoning before serving, if need be.