Pat your steak dry. Season it allllll over on both sides with the Chinese five spice and the salt. Let the steak hang out at room temperature for 20 minutes.
Meanwhile, whisk together all the ingredients for the peanut sauce in a medium mixing bowl. Briefly set aside. Prep your vegetables.
Pre-heat a grill or grill pan over medium-high heat. When hot, add the steak and grill for 2-4 minutes per side for medium-rare. I WISH I could give you a more specific cooking time, but flank steak varies significantly in thickness. I’m sorry! (Mine was a ¼-inch thick and only needed 2 minutes per side.)
Transfer the steak to a cutting board and let it rest for 5 minutes. Slice it in half lengthwise, and then slice cross-wise into ½-inch strips. Transfer the steak to a serving plate/platter.
To assemble your lettuce wraps: Place 2-3 slices of steak on top of each piece of lettuce. Top with some carrots, radishes and scallions. Drizzle with peanut sauce, then sprinkle with chopped peanuts and cilantro. (I recommend letting people assemble their own wraps, but do as you see fit.)