Fry the onion in the oil for a minute to soften. Add the tomato, passata, salt, pepper, chilli powder, and a little hot water and simmer for 15 minutes. Add the fish (if using fillet, it must be defrosted and washed). Add hot water, if needed, to half-cover the fish. Simmer uncovered for 10-15 minutes. Check occasionally to make sure fish is covered with the sauce. Turn over gently if using whole fish, or spoon sauce from the pan over the fish every now and then to make sure it’s covered fully and staying moist.
Taste to check fish is done, add salt if needed. When sauce has thickened, add chopped parsley and lemon juice and move the pan gently in your hands to spread the lemon juice and the sauce evenly. Cover, switch off heat and leave it on the hob for another minute, then serve immediately with fries, fresh bread and a salad.
Note: Optionally, you can throw in a few capers with the lemon juice. Also, you can use cayenne or paprika instead of chilli powder for a mild version. It’s equally mouth-watering!