Halve the onion, then cut each half into crescent moon-shaped wedges about 2cm thick at the thickest part. Heat the oil in a casserole dish. Cook the onion until soft and pale gold, then add the garlic, chillis and ginger, and cook for 2 mins more. Stir in the coconut cream, stock and some seasoning. Heat carefully, but don’t let it boil.
Add the pumpkin and potato, season again, then add the coriander stalks. Simmer until the pumpkin and potatoes are tender. Use a wooden spoon to squash some of the pumpkin if you want to to thicken the stew a little, but don’t break it down too much (you don’t want a purée).
Add the prawns and spinach. Cook gently until the prawns are opaque, about 3 mins. Stir in the lime juice, sugar and fish sauce. Taste the stew, then adjust the flavour with more lime or fish sauce as needed. Roughly chop the coriander leaves, then stir them through. Top each portion of the stew with some sliced red chilli, and serve with lime wedges on the side.
