Pre-heat your oven to 180C Fan/400F/Gas Mark 6
Peel and dice the sweet potato into cubes (roughly 2cm)
Toss the sweet potato in ½ tbsp of vegetable oil then spread out onto a lined baking tray. Cook for 20-25 minutes
While it is cooking, make the curry. Heat another ½ tbsp vegetable oil in a large pan on a low heat
Add the onion, ginger and garlic and cook for 5-8 minutes or until the onion softens (if you want to add fresh chillies add them now with the onion etc.)
Add the curry powder, tumeric and garam masala, stir them in and cook for about 1 minute
Then add the chopped tomatoes, tomato puree and the white fat from the top of the coconut milk can. Stir everything together until the coconut milk melts into the mixture (if you are using frozen spinach add that now)
Bring the curry to a gentle simmer and let simmer, stirring occasionally, for 10-15 minutes
Add the chickpeas and fresh spinach (if using) and stir everything together
Then stir in the sweet potato and cook the curry for another 5 or so minutes until the spinach is wilted
Serve with rice, yoghurt, naan bread etc.
Store fully cooled leftovers in an airtight container in the fridge for up to 2 days or the freezer for up to 3 months