Heat oven to 400° F. Heat 1 tablespoon of the oil in a large ovenproof skillet over medium-high heat. Rub the pork with the thyme, ½ teaspoon salt, and ¼ teaspoon pepper. Cook the pork, turning occasionally, until browned, 6 to 8 minutes.
Transfer the skillet to oven and roast the pork, turning once, until an instant-read thermometer inserted into the center registers 145° F, 12 to 18 minutes. Transfer to a cutting board and let rest for 5 minutes before slicing.
Meanwhile, cook the farro according to the package directions; drain and transfer to a medium bowl. Add the arugula, cherries, lemon juice, the remaining 2 tablespoons of oil, and ¼ teaspoon each salt and pepper.
Serve the farro topped with the sliced pork and any pan juices.