Method:
Whisk together lime juice, fish sauce, soy sauce, sugar, shallot and chiles. Place half of mixture (about 6 tablespoons) in a wide shallow dish and add steak. Cover and marinate, turning occasionally, at least 30 minutes. Chill remaining lime juice mixture separately to dress the salad.
Prepare a grill for high-heat cooking or preheat broiler. Remove steak from marinade; place on grill or broiler pan and cook until desired doneness, 3 to 4 minutes per side for medium-rare. Rest steak 10 minutes, then slice thinly against the grain.
Meanwhile, in a large bowl, combine bok choy, radishes, cucumbers, carrots, basil, mint and cilantro. Toss with reserved lime juice mixture. Spread salad over a large platter and arrange steak over salad.