Preheat grill to medium-high heat. Coat grill rack with cooking spray. Sprinkle steak evenly with 1/4 teaspoon salt and 1/4 teaspoon pepper. Add steak to grill; cook 3 to 4 minutes on each side or until desired degree of doneness. Place steak on a cutting board; let stand 5 minutes. Cut across the grain into thin slices. Combine remaining 1/4 teaspoon salt, remaining 1/4 teaspoon pepper, oil, and vinegar in a large bowl. Add arugula, onion, basil, tomatoes, and cucumber; toss. Add steak and bread cubes; toss. Let stand 10 minutes.