Peel and finely chop the onion. Dice the courgettes. Warm a pan for 1 min. Add ½ tbsp oil and the chopped veg. Season with a little salt and pepper. Cover and sweat over a low heat for 5-6 mins till the veg are soft but have not picked up any colour.
While the veg sweat, finely chop the chilli (flick out the seeds for less heat). Stir most of the chilli into the veg (keep a little for garnishing). Add the coconut milk and 300ml boiling water (or use hot homemade stock). Cover and bring to the boil. Turn the heat down a little and simmer for 5 mins.
Stir the spinach into the soup. Ladle into a blender and blitz, or use a hand-held blender in the pan. Once the soup is smooth, taste and add more salt and pepper if you think it needs it. Ladle into warm bowls and sprinkle with the reserved chilli to serve.