Preheat the slow cooker if necessary; see the manufacturer's instructions. Heat the oil in a frying pan, add the onion and fry, stirring, for 5 minutes or until softened and just beginning to turn golden.
Stir in the paprika and cook for 1 minute, then mix in the beans, mustard, Worcestershire sauce and stock. Bring to the boil, then stir in the tomatoes, red pepper and a little salt and pepper.
Add the frankfurters to the slow cooker pot and tip the baked bean mixture over the top. Cover with the lid and cook on low for 9–10 hours or overnight.
Stir well, then spoon into shallow bowls and serve with buttered toast fingers.