it's ridiculously easy, hence a popular choice around here....
roughly chop the sausage into large bite sized pieces. I put them in a cold non stick pan and then as it heats it releases fat. With some of the raw sausages, I might need to add a little oil. Once they're nice and browned on the outside, remove them to a different pan with a slotted spoon, leaving all the lovely chorizo oil in the pan.
Heat pan up to top whack and fry the aubergine which are ALSO cut into bite sized chunks. Stir them around quickly as they'll immediately absorb the oil, then leave them a bit, moving them less often, until aubergine pieces are all soft and nicely browned on all sides. Throw some salt in at some point during the cooking process.
Put the Chorizo back in and add a tin of cherry tomatoes (I've also done it with fresh cherry tomatoes -then added some passata). Add about a cup of hot water. Generous sprinkle of dried oregano, smoked paprika and a little sugar. (you can add salt and pepper but if I've added salt to the aubergines, and chorizo is quite salty, I don't feel it's necessary) Leave to simmer v gently for 15-20 minutes while you're cooking the pasta (adding a bit more water if necessary - but shouldn't be). Serve with pasta of choice - we usually do penne.
We like to top ours with feta cheese rather than parmesan.
A non-meat version is to use some chopped onion, garlic and fresh chilli in the beginning to replace the chorizo. Then flavour the tomato with more paprika than you would with the chorizo version. This version definitely must have the feta as otherwise we find it's weirdly un-filling, I assume due to lack of protein?