Skin the mackerel and break in into large chunks. Squeeze the orange over it removing any seeds that come in the way.
Slice the onion thinly. You can either halve the olives or slice them into smaller pieces. Add the onions and olives to the mackerel. Tear off the parsley leaves from the harder sprigs and add the tender parts to the mackerel mixture.
Toss all the ingredients well. Now pour in the orange juice and the olive oil and mix well. You can increase the juice quantity according to how tangy you want it to be. Now season with salt and pepper.
The salad is ready. It tastes best with brown bread.