Preheat your oven to 220°C/fan 200°C/gas 7.
Pour 150ml of boiling water over the coconut and leave to soak.
Put your sweet potatoes on a roasting tray and add a good pinch of salt and pepper, the cumin and fennel seeds and a drizzle of olive oil.
Roast in the oven for 20–25 minutes, until soft and sweet in the middle and crispy brown on the outside.
In a large saucepan, sizzle the garlic, ginger, chilli and red onion in a little oil for about 10 minutes, until soft and sweet.
Grind the cumin and coriander seeds in a pestle and mortar, then add to the pan with the other spices and cook for a couple of minutes to toast and release the oils.
Add the lentils, coconut milk and stock to the pan and bring to a simmer, then turn the heat down and bubble away for 25–30 minutes.
While that is cooking make your chutney. Drain the coconut and put it into a bowl.
Fry the mustard seeds and curry leaves in a little oil until they begin to crackle, then pour the mixture over the coconut.
Season with salt and pepper, then stir in the ginger and chilli and give it a good mix.
To finish your dhal, take it off the heat, then stir in the spinach and allow it to wilt a little, stirring in half the chopped coriander and the lemon juice too.
Pile into bowls and top with the crispy sweet potatoes, spoonfuls of the coconut chutney and the remaining coriander.