How to Make It
Heat a large cast-iron skillet over medium-high heat until hot and almost smoking. Brush steak with 1 teaspoon olive oil; sprinkle evenly with 1/2 teaspoon salt and 1/4 teaspoon pepper. Add steak to pan; cook 2 minutes on each side or until desired degree of doneness. Place steak on a cutting board; let rest 5 minutes. Cut across the grain into thin slices.
Combine remaining 1 tablespoon olive oil, remaining 1/4 teaspoon salt, remaining 1/4 teaspoon pepper, and vinegar in a medium bowl, stirring with a whisk. Add onion and tomatoes to bowl; toss to combine.
Divide steak and tomato mixture evenly among 4 serving plates. Sprinkle salads evenly with blue cheese.