Chop the onion and tomatoes, finely chop the garlic. Peel and dice the sweet potato.
Heat a couple of tablespoons of water in the bottom of a medium sized saucepan until bubbling then add the onion. Lower the heat and sauté for 5 minutes, stirring to make sure it doesn’t burn.
Add the chopped tomato, curry leaves and garlic and cook for another 5 minutes, then add the sweet potato. Simmer for a couple of minutes.
Stir in the ground tumeric, lentils or yellow split peas and a good pinch of salt. Leave to cook for a couple of minutes then add the water. Pop on the saucepan lid, bring to the boil, then reduce the heat and simmer for 20 minutes or so until the water is absorbed, the sweet potato soft and the dal is thick and sumptuous.
Add the spinach leaves and cook for another couple of minutes until wilted.
When the dal is nearly cooked. heat a small non-stick pan and add the cumin and black mustard seeds. Once the seeds start to pop and release their aromas (about 1 1/2 minutes), turn off the heat and add the dried red chillis and ginger. Shake the pan and let them cook in the residual pan heat for a couple of minutes
Tip the tempering into the dal, stir well to combine and heat through gently.
Finally, add a squeeze of lemon juice and the fresh chopped coriander then serve.
