1 1/2 pounds flank steak
1 tablespoon thai red curry paste
kosher salt and freshly ground black pepper
1/4 cup salted roasted peanuts, crushed, plus more for topping
1 bunch fresh cilantro leaves, plus more for topping
1 bunch scallions, white and green parts separated
1 pint cherry tomatoes, halved
2 heads boston lettuce, leaves separated
Prepare a grill for direct and indirect heat: For gas grills (with 3 or more burners), turn all the burners to medium-high heat; after about 15 minutes, turn off one of the side burners and turn the remaining burners down to medium. For charcoal grills, bank one chimney starter-full of lit and ashed-over charcoal briquettes to one side of the grill. Set up a drip pan on the other side to avoid flare-ups. (Be sure to consult the grill manufacturer’s guide for best results.) If your grill has a thermometer, aim to keep the temperature at about 350 degrees F throughout grilling.
Set the flank steak on a cutting board. Starting at the thin, narrow end of the steak, slice it in half horizontally to within 2 inches of the opposite wide end. Open it up like a book so you have 1 long piece. Pound the steak with a mallet to an even thickness of about 1/2 inch. Cover the steak with the curry paste and season with 1 teaspoon salt. Sprinkle with the peanuts, leaving a 1-inch border along the edges. Arrange half of the cilantro and scallion greens in a line, followed by half of the tomatoes and then half of the scallion whites. Repeat with the remaining ingredients. Roll up the steak like a jelly roll, starting at the short end. Tie the roll closed around the circumference with butcher’s twine at 2-inch intervals. Tie one more piece of twine lengthwise around the meat. Sprinkle the outside of the meat with salt and pepper.
Put the steak on direct heat and cook, turning, to brown all 4 sides, about 2 minutes per side. Move the steak to indirect heat, cover and cook, turning occasionally, until the very center reads 115 degrees F on an instant-read thermometer for a steak that is well done on the outside and medium rare in the center, 25 to 30 minutes more. (Test frequently; the time will vary based on the temperature of your grill.) Let the steak rest 5 to 6 minutes.
Untie the steak and cut it into thin slices. Serve with the lettuce leaves on the side.