Bruise the cardamom pods and shake out the seeds, then roughly crush them with a pestle and mortar. Peel and chop the onion and sweet potato, peel and finely grate the ginger, then peel and crush the garlic. Heat the oil in a large pan over a low heat. Add the onion and a small pinch of sea salt and cook for 10 minutes, or until soft and sweet, stirring often. Stir in the sweet potato, ginger, garlic and crushed cardamom seeds. Cook for 2 minutes, before adding the coconut milk. Let it simmer for 1 to 2 minutes, then stir in the stock. Cover with a lid, and leave to simmer gently for 15 minutes. Liquidise the soup with a stick blender until smooth, then season to taste with a pinch of salt and black pepper and a squeeze of lemon juice. To make the red pepper topping, heat the oil in a frying pan, then roughly crush and add the coriander seeds and add the chilli flakes. Cook for 1 minute, or until lovely and fragrant. In a dry pan, toast the coconut flakes (if using). Rinse and finely slice the peppers, then add to the spices with the spinach. Continue cooking until the spinach has wilted down, then season and stir in the toasted coconut flakes. Ladle the soup into bowls, finishing with a dollop of red pepper topping, then serve with broken up pieces of poppadoms on the side, if you like.