1/3 cup lime juice
3 tablespoons fish sauce
1 tablespoon reduced-sodium soy sauce
4 teaspoons sugar
1 shallot, finely chopped
1 Thai chiles, stemmed, seeded and finely chopped
2 pounds skirt steak or sirloin flap, cut in 2 pieces
4 cups thinly sliced baby bok choy
6 radishes, halved and thinly sliced
2 small cucumbers, peeled and thinly sliced
2 carrots, grated
1/2 cup lightly packed basil leaves, sliced
1/2 cup lightly packed mint leaves, sliced
1/2 cup lightly packed cilantro leaves, sliced
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.