1. Heat 2 tablespoons of oil in a large saucepan over a medium heat.
2. Peel, finely slice and add the onion along with the curry paste, mix well, then cook for 10 minutes, or until the onion is soft and golden, stirring occasionally.
3. Finely chop the chilli, then peel and finely grate the ginger. Pick the coriander leaves and finely slice the stalks. Chop the sweet potatoes into 2cm chunks.
4. Add the chilli, ginger, coriander stalks and sweet potato to the softened onion. Drain and tip in the chickpeas, then cook for 5 minutes.
5. Roughly chop and add the fresh tomatoes (if using) or tip in the tinned tomatoes. Add 200ml of water and bring to the boil.
6. Reduce the heat to a simmer, then cover and cook for 10 to 15 minutes.
7. Remove the lid, then cook for a further 15 to 20 minutes, stirring occasionally, or until the sweet potato is cooked through and the sauce thickened.
8. Stir in the coconut milk and cook for a couple of minutes, then stir in the spinach and cook until wilted.
9. Scatter over the coriander leaves, then serve with poppadoms and rice, if you like.

Source:

http://www.jamieoliver.com/recipes/vegetables-recipes/sweet-potato-chickpea-amp-spinach-curry/