To make the dhal, heat the oil in a casserole dish or saucepan. Add the onion, along with a pinch of salt, and fry over a medium heat for 10-12 mins or until turning golden and sticky. Add the garlic and ginger and fry for 1 min more.
Add the spices and fry, stirring, for 1 min. Add the lentils, tomato purée, coconut milk and 450ml water, as well as a good pinch of seasoning. Gently simmer, uncovered, for 15-20 mins. Add a splash more water if it starts to stick to the pan.
Heat the oven to 200C/180C fan/gas 6 and line a flat baking sheet with baking parchment. Rub the cauliflower slices with the oil, spices and some seasoning. Lay on the prepared baking sheet and roast for 25-30 mins, or until golden around the edges and cooked through.
Spoon the dhal onto two plates and top with cauliflower steaks. Scatter over the coconut flakes and coriander, and serve with a dollop of yoghurt alongside.
