You'll find rice noodles and curry paste in the Asian section of your grocery store.
Cook noodles according to package directions. Drain and rinse with cold water to prevent noodles from sticking together; reserve.
Combine the curry paste, coconut milk, half the cilantro, lime zest and juice, salt, and pepper in a small bowl; mix well. (This mixture may be made up to 2 days ahead; refrigerate in an airtight container.) Transfer the steak to a roasting pan; rub with 2-3 tablespoons of the curry mixture.
Broil (or grill) the steak until medium-rare (about 4 minutes per side); transfer to a plate.
Arrange scallions, carrots, cucumbers, and reserved noodles on a large platter. Brush steak with more curry sauce. Thinly slice steak, and transfer to the platter. Drizzle remaining sauce over salad; sprinkle with remaining cilantro, peanuts, and mint.