Place the beef stock, carrots and 1 tbsp soy sauce in a large saucepan and gently bring to the boil, covered. Cook gently for 5 minutes.
Meanwhile, mix the ginger, oil and remaining soy in a bowl and add the steak strips.
Add the pak choi and noodles to the soup and cook for a further 2-3 minutes. Meanwhile, heat a frying pan and fry the steak for 4-6 minutes until browned, then stir into the soup. Divide between 4 bowls and sprinkle over some sesame seeds to serve.