Peel the pumpkin with a vegetable peeler or a sharp knife.
Cut in half and scoop out the seeds with a spoon. Cut the flesh into 1cm cubes. Place on a baking tray and roast in a preheated oven at 220°C (200°C fan, gas 7).
Meanwhile, peel and finely dice the onions. Peel the garlic and ginger and chop finely. Heat the oil in a large pan and fry the ginger, onion and garlic over a medium heat for 5 minutes.
Add the roast pumpkin and vegetable stock and bring to the boil. Wash, deseed and finely chop the chillies.
Simmer the soup for 20 minutes. Puree the soup in the pan with a stick blender, then press through a sieve.
Return the soup to the pan and reheat gently. Squeeze the juice from the lime and use to season the soup along with salt, pepper and the chilli.
Toast the sesame seeds in a dry pan until aromatic. Wash the coriander, shake dry and pick off the leaves. Sprinkle the sesame seeds and coriander over the soup and serve.