Rinse and drain the farro and place it in a large saucepan with 4 cups water and 2 teaspoons salt. Bring to a boil, lower the heat, cover, and simmer for about 20 minutes, until tender. Drain.
Meanwhile, combine the cucumbers, chickpeas, scallions, parsley, and mint in a very large bowl.
In a 2-cup glass measuring cup, whisk together the olive oil, lemon juice, 2 teaspoons salt, and 1 teaspoon pepper. Add the hot farro to the vegetables and herbs, pour the dressing on top, and stir to combine. Carefully stir in the feta, olives, 2 teaspoons salt, and 1 teaspoon pepper. Serve at room temperature.