Preparation Stir together soy sauce, vinegar, ginger, garlic, Sriracha, sugar, and sesame oil. Prepare a gas grill for direct-heat cooking over medium-high heat. Oil grill rack, then grill steak, covered, turning over once, 6 to 8 minutes for medium-rare. Transfer steak to a cutting board and drizzle with 2 tablespoons sauce, then let stand, uncovered, 5 minutes. Thinly slice steak across the grain. Serve with remaining sauce, scallions, and sesame seeds.
Preparation Stir together soy sauce, vinegar, ginger, garlic, Sriracha, sugar, and sesame oil. Prepare a gas grill for direct-heat cooking over medium-high heat. Oil grill rack, then grill steak, covered, turning over once, 6 to 8 minutes for medium-rare. Transfer steak to a cutting board and drizzle with 2 tablespoons sauce, then let stand, uncovered, 5 minutes. Thinly slice steak across the grain. Serve with remaining sauce, scallions, and sesame seeds.