Cut the steak against the grain into 6mm-thick slices. Use a meat mallet to pound the slices until 3mm thick. Place slices in a large bowl. In a medium bowl, whisk mandarin rind, mandarin juice, ginger, garlic, chilli, honey, soy sauce and 1 tbs of the oil. Add 11/2 tbs of the mandarin mixture to the steak in the bowl. Cover and marinate the steak for at least 1 hour. Reserve remaining mandarin mixture.
Heat a chargrill on medium-high. Place buk choy and remaining oil in a bowl and toss to coat. Season with salt. Cook buk choy on grill for 1 min each side or until grill marks form. Transfer to a chopping board and cut out the cores. Return the buk choy to the bowl. Toss with half the reserved mandarin mixture.
Remove the steak from the bowl and pat dry with paper towel. Season with salt. Heat the chargrill on high. Cook the steak on the grill, in batches, for 30 secs each side or until grill marks form and the steak is cooked to medium-rare. Transfer to a chopping board and set aside for 2 mins to rest. Cut the beef into bite-size pieces and toss with the remaining reserved mandarin mixture.
Meanwhile, to make the carrot salad, combine the carrot, sesame seeds and oil in a small bowl. Season with salt.
Divide the rice, buk choy, carrot mixture and steak among serving bowls. Spoon over any juices from the steak. Top each with an egg and sprinkle with the spring onion.