Heat 2 tbsp olive oil in a non-stick pan on medium heat. Add the onion and fry for 5 minutes until translucent. Add the chopped chorizo and fry for 5 minutes until the chorizo is softly cooked. Add 3 or 4 tbsp of the relish and the potatoes and toss well to coat together. Season with salt and pepper to taste and cook on a medium-high heat for a further 5 minutes. Toss the asparagus in a little olive oil, and season with salt and pepper. Fry in a ribbed skillet pan on medium-high heat for 5 minutes, until slightly blackened and just-cooked. Transfer the potato and chorizo mix, and combine with asparagus into a large ovenproof dish. Cook in a pre-heated oven (200c / 180c fan) for 10 minutes. Sprinkle generously with parsley before serving with an extra dollop of the relish.