In a wide heavy-based pan, fry the onion in the oil with a lid on to soften for about 5 minutes. Stir in the sweet potato chunks, curry powder and turmeric and fast fry with the lid off until it begins to stick to the bottom.
In batches, stir in the spinach, adding the ground almonds and chilli. When the spinach is all in the pot and begins to collapse, pour in the coconut milk, add some salt, stir well and put the lid back on.
Keep it at an active simmer, stirring from time to time, for about 20 minutes until the potatoes are cooked. Take the lid off and let the curry reduce down to a thicker consistency (NB – only if the sauce looks like it needs it!)
Finish the curry by stirring in the lime juice and adjust seasoning to taste.