Heat 2 tablespoons of the rapeseed oil in a pan. Add the red onions, chillies and garlic and cook over a high heat for 5 minutes, until they are starting to catch, stirring quite frequently to prevent the mixture from sticking. Pour in the vinegar and boil fast for about 2 minutes, until it has evaporated. Transfer to a large bowl and leave to sit for 15 minutes before giving it another stir. Season to taste.
Heat the remaining tablespoon of rapeseed oil in the frying pan and add the chorizo. Fry for a few minutes to release the fats, then add the chickpeas and continue to cook for a few minutes, until the chorizo is cooked through. Tip into the onion and chilli mixture in the bowl and toss until well combined.
Fold the herbs into the salad with the feta cheese and spring onions, tossing until well coated. Season to taste and divide between plates to serve.