Serving a small portion of lean steak over a bed of arugula is an affordable, healthful way to eat red meat. An ample side of veggies further boosts nutrition.
Juice one lemon half into a shallow dish or zip-top bag large enough to hold steak. Add 2 tablespoons extra virgin olive oil, the garlic, rosemary, 1 teaspoon kosher salt, and several grinds of black pepper; mix well to combine.
Add flank steak and coat well, using your hands to rub marinade into meat. Cover or seal; refrigerate 1 to 24 hours.
Place a rack in top third of oven. Place a large cast-iron skillet or a roasting pan on rack and preheat oven to 450°F. Let skillet heat for 30 minutes. Meanwhile, take steak out of refrigerator to rest.
Place steak in skillet, and return skillet to oven. Cook 5 minutes, flip steak, then continue to cook until nicely browned and firm, 2 to 4 minutes more. An instant-read thermometer should read 120°F to 125°F for a medium-rare (130°F to 135°F for medium). Transfer steak to a cutting board; let rest 10 minutes.
Meanwhile, in a large bowl, combine 1 tablespoon olive oil, the juice from the remaining lemon half, and a pinch kosher salt. Add arugula; toss to coat. Spread arugula on a platter.
Thinly slice steak against grain and arrange on arugula. Top with shaved Parmesan as well as a few grinds of black pepper. Serves 4.