Heat the oil in a large saucepan, add the onion and fry for 3 minutes. Add the garlic and fry for 2 minutes. Add the chopped tomatoes and tomato purée, along with 400ml cold water, bring to the boil then simmer for 20 minutes until thickened.
Add the peppers and cod, nudging the fish into the sauce a little, then bring back to a gentle boil and simmer for 8 minutes. Scatter with the olives and parsley, and simmer for 2 minutes. Meanwhile, cook the rice to pack instructions.