Place a large saucepan over a medium heat. Add the oil and then the leeks or onions, garlic, bay leaves if using, and curry powder or paste. Sweat, stirring regularly, for 3-4 minutes.
Pour in the milk and stock, bring to a simmer and cook for a further 2–3 minutes.
Add the smoked fish and beans followed by the spinach, adding it a handful at a time as it wilts down in the simmering soup. By the time the spinach is wilted (in just a few minutes), the fish will be cooked.
Add the chopped parsley or coriander if using, and season with a few twists of pepper (the smoked fish should make it salty enough). Ladle into warm bowls and serve.