How to Make It
Heat a skillet over medium-high. Coat pan with cooking spray. Sprinkle steak with 1/4 teaspoon salt and black pepper. Add steak to pan; cook 4 to 5 minutes on each side for medium-rare or until desired degree of doneness. Place steak on a cutting board; let stand 5 minutes. Cut across the grain into thin slices.
Place remaining 1/4 teaspoon salt, oil, parsley, vinegar, capers, garlic, and crushed red pepper in a bowl, stirring with a whisk. Divide arugula evenly among 4 plates. Top evenly with steak, onion, and cheese. Drizzle evenly with oil mixture.