Heat olive oil in a medium pot over medium heat, just until simmering. Add the onion and sauté until softened. Add garlic and ginger, and cook 2 -3 more minutes, stirring.
Pour in coconut milk, bring to the boil and simmer for 3-5 minutes to reduce slightly, then add the cod. Cover and simmer 8 – 10 minutes until cod is cooked.
Add spinach and cook 3 – 5 more minutes just until spinach is wilted.
through. Season with salt and pepper to taste.