Soak the beans overnight in plenty of fresh cold water. The next day, preheat the slow cooker to low. Heat the olive oil in a frying pan over low–medium heat, add the onion and cook for about 5 ...
Fill the tomato tin with water and pour into the slow cooker pot. Half fill the can again and add this too (this should make 600ml/20fl oz water in total). Add the chorizo, beans, paprika ...