A steak sammie is always a good idea. This one gets a kick from horseradish, blue cheese, red onion, and watercress.
Season steak. In skillet, cook steak in oil over medium-high until medium-rare, about 4 minutes per side. Let rest for 5 minutes. Thinly slice. In bowl, mix mayonnaise, cheese, and horseradish; season. Spread on rolls. Top with steak, watercress, and onion.