Cook the farro according to package directions. Drain and set aside. Drizzle with two tablespoons of olive oil so the farro does not stick together.
Heat 2 tablespoons of olive oil in a large skillet over medium-high heat. Once hot, add the sliced red onions, a pinch of sugar and salt. Fry for about 10 – 15 minutes or until the onions have caramelized, stirring frequently. Turn the heat down if they are cooking too quickly. The onions are done when they have completely wilted, or softened. Remove from the heat and set aside.
In a large bowl, combine the cooked farro and onions, remaining 2 tablespoons of olive oil, arugula and feta. Taste and adjust the salt and pepper as you like and also feel free to add more olive oil if you wish. Enjoy immediately or cover with plastic wrap and keep in the fridge until ready to serve.