Mackerel and rice? Another one pan job.
Sweat a large onion for a couple of minutes in plenty of olive oil, chuck in a tin of sweetcorn, chuck in a tin of chickpeas, maybe chuck in a bit of ginger, break up a pack of peppered mackerel and chuck it in, stir it and heat for a couple of minutes, chuck in a cup of rice and stir and heat until the rice goes translucenty, chuck in twice as much water as you did rice.
Bring to the boil, chuck a lid on and simmer on lowest heat setting for twenty minutes. Turn the heat off and let it stand for five minutes.
Chuck it on a plate or in a bowl.