Thinly slice 1/4 of the red onion and add it to a bowl. Add the juice from half of the lime and a pinch of salt, give it a stir, then set aside to pickle.
Finely chop the remaining red onion and half of the red chilli. Add 2 tablespoons of coconut oil to a casserole pot or large pan on a medium heat, then add the cumin seeds and cook for 1 minute to lightly toast the seeds.
Next add the chopped red onion and red chilli, along with the garlic and ginger. Cook for 7-8 minutes or until the onion is nicely caramelised.
Stir in the curry powder and cook for a minute. Next add the tinned tomatoes, then fill a quarter of the empty tin with water and swirl it around to collect any leftover tomato juices, before pouring the water into the pot, followed by the butter beans and a generous pinch of salt. Stir, then cover with a lid and cook for 25-30 minutes or until it has thickened.
Finally, stir in the yoghurt, maple syrup and the juice from the remaining half of lime. Give the curry a stir and season with extra salt, if necessary, then cook for another 2-3 minutes before removing from the heat.
Slice the remaining half of red chilli, then use it to top the curry along with some more yoghurt, the coriander, pickled red onion and nigella seeds. We love to serve with cooked rice and warm bread or naan. Yum!