Crumble the stock cube into a heatproof jug. Pour in 1.2 ltrs boiling water and stir to dissolve the stock cube. Set aside.
Peel the zest from the lime using a veg peeler (keep the lime for later). Peel and slice the shallot. Peel and grate the ginger. Finely slice the chilli (flick out the seeds and white bits for less heat).
Put the lime zest, shallot, ginger and ¾ of the chilli in a large pan. Pour in the stock. Drop in 2 star anise and 1 tsp peppercorns, if you’re using them. Cover. Bring the stock to a gentle boil. Carefully slide in the chicken breasts and pop on a lid. Leave to simmer for 20 mins.
Meanwhile, juice the zested lime into a bowl. Peel and finely slice the red onion. Add to the lime juice with a pinch of salt and scrunch together. Leave to one side to marinate.
Peel the carrot. Use a vegetable peeler to peel ribbons from the carrot, turning it as you go till you get down to the core. Finely slice the core. Finely slice the cabbage half, discarding any really thick pieces of core.
Once the chicken has poached for 20 mins, lift it from the stock and pop on a plate. Pour the stock through a sieve into a jug, pushing the fragrant spices with the back of a spoon to release more flavour. Discard the contents of the sieve.
Pour the stock back into the pan and keep on a low heat. Add the carrot and cabbage to the stock. Simmer for 5 mins.
While the veg simmer, use a couple of forks to shred the chicken into small pieces (or finely slice it if you prefer).
Add the noodles to the pan. Simmer for 3-4 mins till the noodles are cooked. Ladle into warm bowls, top with the chicken, the onion and its limey marinade. Garnish with the remaining chilli slices and serve.