Ingredients

• 2 tablespoons Worcestershire sauce
• 2 tablespoons fresh lemon juice
• 2 tablespoons olive oil
• 1 garlic clove, minced
• 2 teaspoons sugar
• 1 pound flank steak (3/4 inch thick)
• 1 medium shallot, finely chopped
• 3 tablespoons red-wine vinegar
• 1/2 teaspoon Dijon mustard
• 4 tablespoons extra-virgin olive oil, divided
• 1 very large red onion, halved and sliced 1/3 inch thick
• 3/4 pound bitter greens such as escarole or frisée or a combination
• Equipment: a grill basket

Instructions

1. Whisk together Worcestershire sauce, lemon juice, oil, garlic, and sugar in a shallow dish. Add steak, turning to coat, and marinate at room temperature 15 minutes.
2. Make dressing and prepare onion while steak marinates: Whisk together shallot, vinegar, mustard, 3 tablespoon oil, 1/2 teaspoon salt, and 1/4 teaspoon pepper in a large bowl. Toss onion with remaining tablespoon oil and 1/4 teaspoon salt in a small bowl.
3. Whisk together shallot, vinegar, mustard, 3 tablespoon oil, 1/2 teaspoon salt, and 1/4 teaspoon pepper in a large bowl. Toss onion with remaining tablespoon oil and 1/4 teaspoon salt in a small bowl.
4. Grill steak and onion: Prepare a gas grill for direct-heat cooking over medium-high heat. Pat steak dry and season with 1/4 teaspoon each of salt and pepper. Oil grill rack. Grill steak, covered, turning once, 8 to 10 minutes total for medium-rare. Transfer steak to a cutting board and let rest, uncovered, 5 minutes. While steak rests, grill onion in grill basket, covered, stirring occasionally, until charred and tender, 4 to 5 minutes. Thinly slice steak across the grain. Toss greens, onion, and steak with dressing and salt to taste.
5. Prepare a gas grill for direct-heat cooking over medium-high heat. Pat steak dry and season with 1/4 teaspoon each of salt and pepper. Oil grill rack. Grill steak, covered, turning once, 8 to 10 minutes total for medium-rare.
6. Transfer steak to a cutting board and let rest, uncovered, 5 minutes.
7. While steak rests, grill onion in grill basket, covered, stirring occasionally, until charred and tender, 4 to 5 minutes.
8. Thinly slice steak across the grain. Toss greens, onion, and steak with dressing and salt to taste.