Prep: 1. Mound arugula on a large platter. 2. Cut steak crosswise (against the grain) into 1/8-inch-thick slices; season with salt and pepper. 3. Smash garlic. Make: 1. Heat oil, garlic and rosemary in a large pan over high heat, until garlic is golden, about 4 minutes. Discard garlic and rosemary. 2. Add meat to skillet; sauté over high heat, tossing with tongs to color evenly, about 1 minute for medium-rare. 3. Remove from pan and arrange steak over arugula. 4. Add shallot, vinegar, salt and pepper to oil in pan; cook for 2 minutes until reduced. Serve: Pour dressing over steak and serve immediately.
If you prefer rare meat leave the steak whole while it cooks for about 3 minutes per side depending on the thickness, and then slice after cooking.