Heat oven to 220C/200C fan/gas 7. Put the sweet potatoes on a baking tray and bake for 40 mins or until soft. Meanwhile, heat the oil in large non-stick saucepan over a medium-high heat. Fry the onion for 3-5 mins or until pale golden brown, stirring constantly, making sure it doesn’t burn. Add the garlic, ginger, chilli and spices, and cook for a few secs, stirring constantly.
Add the lentils to the pan, pour over 400ml water, stir well and bring to the boil. Skim off any foam that rises to surface with a spoon. Add 1 /2 tsp flaked sea salt, the lemon zest and 1 tbsp of the lemon juice, stir well and reduce the heat to low.
Cover the pan loosely with a lid and leave to simmer gently for 20 mins or until the lentils are tender, stirring occasionally. Add the tomatoes, coriander and remaining 1 tbsp lemon juice, and cook for a further 5 mins, stirring. If the lentils thicken too much, add a splash of water. Season to taste.
To make the red cabbage slaw, whisk the oil and lemon juice together in a large bowl and season with lots of ground black pepper. Add the cabbage, carrot, spring onions, sultanas and seeds, then toss together well.
Put the potatoes on two plates, split them and fill with the lentils. Spoon over the yogurt, garnish with coriander and serve with the coleslaw and lemon wedges for squeezing over, if you like.