1.Heat oil in a large saucepan and gently cook chilli, onion, ginger and garlic for 5 minutes.
2.Add coriander, turmeric and cumin and stir for 1 minute.
3.Add fish sauce, brown sugar, lemongrass, coconut milk, lemon juice, tomato paste, pumpkin and potatoes. Bring to the boil and simmer until potatoes are just tender.
4.Serve with rice and garnished with coriander leaves.