Cut 2 pocket breads (7 in.) into 1-inch squares. Put in a zip-lock plastic bag with 2 teaspoons olive oil; seal bag and turn to coat. Pour pieces into a 10- by 15-inch baking pan and spread into a single layer. Bake in a 450º oven until crisp and lightly browned, about 5 minutes. Let cool at least 10 minutes. Meanwhile, in a large bowl, mix 2 tablespoons lemon juice, 2 tablespoons extra-virgin olive oil, 1/2 teaspoon salt, 1/4 teaspoon coarse-ground pepper, and 1/8 teaspoon ground sumac (optional; available in markets that carry Mediterranean ingredients). Add 3 cups bite-size pieces of rinsed and crisped romaine lettuce leaves (about 4 oz.); half an English cucumber, rinsed, quartered lengthwise, and cut into 1/2-inch chunks; 2 cups cherry tomatoes, rinsed and stemmed (cut in half if larger than 3/4 in.); half a sweet onion (8 oz.), thinly slivered; 1/2 cup Italian parsley leaves; 3 tablespoons chopped fresh mint leaves; and the pocket-bread chips. Mix gently to coat.