Bring the peas or fava beans to the boil with the water and skim off any scum that appears. Simmer for between 40 minutes and 1 hour. In a large saucepan, heat the olive oil over a medium heat. Add the onion with a pinch of salt and cook for about 15 minutes, stirring occasionally, until sweet and golden. Now add the garlic and cumin and fry for another 2 minutes until brown. Remove from the heat and add the dried chilli. When your beans are cooked they should be soft. Mix in the onion mixture and simmer for another 5 minutes. If you like a very smooth-textured soup, whizz with a hand-held blender or in a food processor. Season with salt and pepper and stir in the fresh coriander. If the soup is too thick, simply add more water and adjust the seasoning (it should be the consistency of double cream). Ladle into bowls and drizzle the argan/olive oil mix on top.