1Preheat an outdoor grill for medium-high heat and lightly oil the grate. Sprinkle pepper and salt onto flank steak.
2Cook steak on preheated grill until desired doneness is reached, 5 to 6 minutes per side. An instant-read thermometer inserted into the center should read 140 degrees F (60 degrees C).
3Whisk lime juice, soy sauce, brown sugar, fish sauce, garlic, and chile-garlic sauce together in a bowl.
4Mix romaine lettuce, mint, cilantro, and basil together in a bowl; spoon about 6 tablespoons lime juice mixture over romaine mixture. Toss to coat.
5Cut steak into strips and place strips into remaining lime juice mixture; let sit for steak to marinate, 1 to 2 minutes. Place steak on romaine mixture.