Heat the olive oil in a large pan over medium-high heat.
Add the chorizo and cook, stirring, until most of the fat is rendered and it begins to crisp on the edges. Transfer the chorizo to a bowl and set aside.
Add the onions the pan and cook until they start to soften.
Add the garlic and cook for a few seconds before adding the chopped tomatoes with juices.
Season with salt & pepper to taste and allow to cook for around 10 minutes on a low heat.
Increase the heat before adding the wine and tomato relish and stir to combine.
Add the mussels, then cover with a lid and cook for 3 minutes, shaking the pan.
Add the chorizo back into the pan and discard any unopened mussels.
Serve with rustic bread and a sprinkling of fresh parsley.