Step 1Heat half of the oil in a wok or large non-stick frying pan over medium heat. Add the onions and cook, stirring, for 2–3 minutes until softened, then add the corn and bok choy. Cook for 5 minutes, or until tender. Add curry paste; cook for 1 more minute. Reduce heat to low; stir in the coconut milk, the fish sauce and 1 cup of water, and bring to a simmer. Keep the heat low to prevent the coconut milk splitting.
Step 2Meanwhile, cook basmati rice according to packet instructions. At the same time, heat a medium non-stick frying pan over a high heat. Rub the steaks with the remaining oil, then cook for 2–3 minutes on each side, for medium, or done to your liking. Set aside to rest for 5 minutes.
Step 3Stir the lime juice and most of the coriander into the curry, then season with cracked black pepper. Slice the steaks, then stir them into the curry along with any resting juices. Serve topped with the remaining coriander and chilli oil (if using), with the rice set out alongside.