Place oil in a heavy based pan over medium heat. Add cumin seeds, fenugreek seed, mustard seeds and cook 1-2 minutes.

Add chopped onion and sauté for approx. 5 minutes, or until slightly brown.

Add chilli, ginger, tomatoes and cook for a further 5 minutes.

Add dried spices, salt, coconut sugar and curry leaves. Stir and cook another minute or so.

Add sweet potato, coating well with sauce. Reduce heat and cook for 30 - 40 minutes, or until sweet potato is tender.

Add lime juice and garnish with coriander.  Serve with fragrant basmati rice and/or spiced roti.