In a large ovenproof skillet, heat oil over medium-high heat. Sprinkle steak with ¾ teaspoon salt and ½ teaspoon pepper. Add steak to skillet, and cook until browned, about 3 minutes per side.
Bake for 10 minutes or until desired degree of doneness. Transfer to cutting board, and let stand for 15 minutes; thinly slice.
In a small bowl, whisk together ½ cup blue cheese, mayonnaise, milk, vinegar, and remaining ¼ teaspoon each salt and pepper. Arrange lettuce, spinach, and tomatoes on a large serving platter, and top with steak, onion, and remaining ½ cup blue cheese. Serve with blue cheese dressing.
Recipe by Paula Deen Magazine at https://pauladeenmagazine.com/steak-blue-cheese-salad-recipe/