How to Make It
Combine the tomatoes, garlic, vinegar, 3 tablespoons of the oil, and ¼ teaspoon each salt and pepper in a medium bowl. Let sit, stirring occasionally, until the flavors meld, about 10 minutes. Add the Feta, herbs, and arugula and toss to combine.
Meanwhile, heat the remaining tablespoon of oil in a large skillet over medium-high heat. Season the steak with ½ teaspoon salt and ¼ teaspoon pepper. Cook until an instant-read thermometer inserted into the thickest steak registers 130° F, 2 to 5 minutes per side for medium-rare. Let rest for 5 minutes before slicing against the grain.
Serve the steak with the tomato and arugula salad.