Rinse the farro well. Bring the orange juice and water to a boil in a large saucepan. Add a big pinch of salt and pepper. Once boiling, stir in the rinsed farro. Reduce the mixture to a simmer and cook for 25 to 30 minutes, until the farro is chewy and tender. Drain the farro and place it in a large bowl.
Add the arugula to the farro. Drizzle in a few tablespoons of the dressing, just to coat the farro and arugula. Top with the oranges, pistachios, celery and feta. Toss well. Taste and season with salt and pepper as needed.
Serve! This stays great in the fridge for a few days too.
