Cook the onions and spices: Put the lentils into a bowl and pour over enough cold water to cover them by about 1cm. Leave to soak while cooking the onion and spices. Heat the oil in a large heavy-based pan, add the onion and gently cook for 5 minutes or until almost soft, stirring occasionally. Add the garlic, ginger, cumin and turmeric. Cook for 1 minute, stirring all the time.
Add the lentils: Drain the lentils and add to the pan with the coconut milk, vegetable stock and seasoning. Bring to the boil, then reduce the heat, half-cover the pan with a lid and simmer for 5 minutes.
Prepare the tomatoes: While the lentils are simmering, put the tomatoes into a heatproof bowl and pour over boiling water to cover. Leave for 1 minute, then remove with a draining spoon and rinse briefly under cold water. Peel off the skins and dice the flesh.
Complete the cooking: Add the tomatoes to the lentil mixture with the lime or lemon juice. Re-cover the pan and simmer for a further 10 minutes. Stir in the courgettes and cook, stirring occasionally, for a further 5 minutes or until the lentils are tender and the dhal thick and creamy. Taste and adjust the seasoning if necessary, then stir in the coriander before serving, if you like.
The dal can be made up to 24 hours beforehand, stored in the fridge, or frozen for up to three months. Thaw if frozen, reheat with an extra 2 tbsp vegetable stock or water, and simmer for 1-2 minutes.
Lentil bolognese: Pour 500ml boiling vegetable stock, made with stock cubes, over 225g split red lentils and leave to soak. Heat 2 tbsp olive oil in a large pan and gently cook 1 large chopped onion for 5 minutes or until almost tender. Stir in 2 crushed garlic cloves and a pinch of ground cinnamon and cook for a few seconds. Add the lentils and stock to the pan with a 400g chopped tomatoes with basil. Stir, then half-cover the pan with a lid and cook for 15 minutes or until the lentils are tender. Season to taste and serve on top of pasta.