I started making it years ago from a recipe, but just feel it as i go now. It's all from the freezer or cupboard, except for the chorizo.
Slice and fry half a ring of chorizo fairly gently until it's given up a nice bit of fat. Then lift the chorizo out, and fry half a bag of frozen soffrito mix for a few minutes in the fat. Add a good squirt of tomato puree (probably 2 or 3 tablespoons), and fry that off over a medium heat for just a minute or two as you stir it, before adding two tins of chopped tomatoes. Then add some stock to loosen it a bit (I used about half a pint of vegetable stock, but possibly could have used a little less), bring to a simmer for a few minutes before adding about half a bag of frozen sliced veg, putting the chorizo back in, and bring it back to a simmer for a few minutes. Then I added four frozen cod fillets, made sure they were submerged in the liquid, brought if back to a simmer, and left it for about 15-20 minutes. I personally find that thanks to the chorizo I didn't need any salt at all, but it does benefit from a good bit of black pepper. And I'm sure a bit of parsley would be nice, but we didn't have any.
Sorry it's a bit vague with 'half a bag' etc, but they were M&S standard size bags - their soffrito mix, and a bag of chargrilled aubergines, courgettes and peppers. Another advantage of which is that apart from the chorizo and boiling a kettle for the stock pot. I did consider buying those little trays of diced chorizo, but I prefer it a bit chunkier so bought a ring instead.
It would serve four generously enough I'd say with some nice bread, but we ate a little too much last night, hence adding a jar of butter beans today, which you'd never know weren't originally intended to be there from the start to be honest. And I think i may put in intentionally the next time I make it.