Place noodles in a heatproof bowl. Cover with boiling water. Stand for 5 minutes or until tender, adding choy sum stems during last 2 minutes. Using a fork, separate noodles. Drain. Refresh under cold water. Drain well.
Heat a wok over high heat. Add oil. Swirl to coat. Add egg, swirling wok so egg covers base. Cook for 1 to 2 minutes or until set. Slide onto a board.
Make Dressing: Combine all ingredients and 3 teaspoons water in a screw-top jar. Secure lid. Shake until sugar has dissolved.
Roll up omelette. Thinly slice. Using a julienne peeler, cut carrot into long, thin strips. Place noodle mixture, choy sum leaves, carrot, mint and coriander in a large serving bowl. Gently toss to combine. Top with sliced omelette. Drizzle with dressing and sprinkle with peanuts. Serve.
