Heat the sesame oil, sauté the garlic and ginger and deglaze with 500 ml stock. Add the chilli flakes and bring to the boil briefly. Add the chicken and cook over a low heat for 10-15 minutes.
In the meantime, prepare the pasta in a separate saucepan.
Add the rest of the broth. Add the carrots, bell peppers and snow peas and cook for about 3-5 minutes. Add the leek and cook for another 2 minutes. Season to taste with salt and soy sauce.
Lift the meat out of the soup, cut into pieces and put back into the soup. Remove the lemongrass before serving. Put the noodles in a deep plate or a soup bowl, pour the soup over it, garnish with coriander and serve.
Variation: instead of the chicken, cook scampi for 10 minutes.