Prepare noodles according to packet instructions. Drain and set aside.
Meanwhile, place stock into a large saucepan. Add two cups (500ml) water, ginger, star anise, cinnamon and fish sauce. Bring to the boil over high heat before reducing heat to a simmer. Simmer, uncovered, for 20 minutes. Strain broth and return to pan. Return broth to the boil, add onions, greens and mushrooms and simmer for 2-3 minutes or until softened.
Divide noodles and ¾ of sprouts between four large soup bowls. Top with lamb and ladle over hot broth. Serve topped with remaining sprouts and your choice of sliced chilli, coriander, Thai basil, chilli sauce and lemon wedges.
Place the meat in the freezer for 15 minutes before slicing to make it easier to achieve paper-thin slices.
For tender lamb, ensure you slice the meat against the grain.
Lamb rump, backstrap or leg steaks or would also work well in this recipe.
Serve with hoisin sauce, if desired, for extra sweetness.