In a large bowl, place cod, lime zest and juice. Season with salt and black pepper. Toss to combine, cover and set aside to marinate for 15 minutes.
In a large, deep skillet or pan, heat olive oil over medium heat. Add onion and bell peppers and cook until softened, about 5 minutes.
Add garlic, paprika, coriander and chili flakes. Cook for another 1 to 2 minutes. Add chopped tomatoes and tomato purée and simmer over medium, stirring occasionally, until most of the liquid has evaporated and mixture has thickened, about 6 to 8 minutes.
Pour in coconut milk and stock. Bring to a boil, then reduce heat. Add the marinated fish and shrimp and simmer on a low heat until just cooked through, about 5 minutes.
Stir in remaining lime juice and zest and garnish with parsley. Serve on its own with lime wedges, or with crusty bread.