Heat the oil in a large saucepan. Add the onion to the pan and fry for 2mins until just softened. Add the sweet potato into the saucepan and fry for another 2mins. Stir through the curry powder, frying for 30sec until fragrant.

Then stir in the tomatoes, coconut milk and water. Bring to the boil and then reduce to a simmer for 15mins.

Stir through the brown lentils and green beans, simmer for another 5mins and then serve.