Mix the five-spice with 1/2 tsp flaky sea salt and 1/2 tsp black pepper, and rub into the steaks. Heat 1 tsp of the oil in a large, non-stick frying pan over a medium-high heat. Fry the steak for 4-5 mins each side or until done to your liking. Transfer to a warmed plate, cover loosely with foil and leave to rest.
Pour the remaining oil into the pan, add the pak choi, the carrot and pepper. Stir-fry for 3 mins, then add the noodles and stir-fry for 2 mins more.
Pour in the teriyaki sauce and simmer for a few secs, then divide the vegetable noodles between 2 warmed plates or shallow bowls. Slice the steak thickly and place on top.