Peel and finely slice the onions, garlic and ginger. Cut the courgette into bite-size pieces and roughly chop the tomatoes
Saute the onions, garlic and ginger in 4 tbsp of water in a large pan on a high heat for 5 minutes. Stir regularly, adding more water if they start to stick to the bottom of the pan. When the onions are soft, add the courgette, tomatoes, sweet potatoes and 1 tsp salt. Cover the pan and cook gently over a low heat for 5-10 minutes, stirring occasionally.
Add the lentils, spices, tamari, lime juice, the remaining salt and 2 litres of water, and bring to the boil. Reduce to a low heat and simmer for 25 minutes, or until you are happy with the texture of the dahl. Stir regularly, as lentils have a tendency to stick
Finely chop the coriander and sprinkle over the dahl. Serve with brown rice or toasted wholemeal pitta breads, cut into soldiers. Mango chutney is also a nice accompaniment.