Heat the oil in a large pot or deep frying pan and add the onion. Cook over a medium heat for 8 minutes, until softened but not coloured.
Add the garlic, ginger, fish sauce and curry paste and stir to combine.
Add the stock, coconut milk and lime leaves and bring to a simmer for 5 minutes.
Add the kūmara and cook for a further 15 minutes, or until just cooked through.
Add the lentils and beans, cook for a final 5 minutes, then serve immediately.
