Bring a 3 quarts water to a boil with 1 tablespoon salt; add the farro. Lower the heat to a simmer and cook until the farro has swelled and softened but still has a little bite, about 20 minutes. Drain.
While the farro cooks, combine the cucumbers, tomatoes and garlic in a large bowl. Add the lemon juice, olive oil, cumin and salt to taste; toss gently.
Add the warm drained farro to the tomato mixture, sprinkle the herbs over and toss together. Crumble the feta cheese over the salad.