How to Make It
In a large saucepan, heat 2 tablespoons of the oil. Add the yellow onion, carrot and celery, cover and cook over moderately low heat until barely softened, about 5 minutes. Add the farro and stir to coat with oil. Add the water and bring to a boil. Cover and simmer over low heat until the farro is barely tender, about 10 minutes; season with salt. Cover and simmer until the farro is al dente, about 10 minutes longer. Drain the farro and discard the onion, carrot and celery. Let cool completely.
In a large bowl, whisk the remaining 1/3 cup of olive oil with the vinegar and season with salt and pepper. Fold in the farro, red onion, cucumber, tomatoes and basil, season with salt and pepper and serve.