Season steak with salt and pepper. In a large skillet, heat oil over medium heat. Add steak; cook 5-7 minutes on each side until meat reaches desired doneness (for medium-rare, a thermometer should read 135°; medium, 140°; medium-well, 145°). Remove from pan; let stand 5 minutes. Cut steak into bite-sized strips; toss with lime juice., On a platter, combine romaine, strawberries and onion; top with steak. Sprinkle with cheese and walnuts. Serve with vinaigrette.