Chop the onion finely. Drain and rinse the beans. Drizzle the oil in the pan and heat. Add the chopped onion and sauté for a few minutes at medium heat.
Mix the tomatoes, ½ cup of barbecue sauce, mustard, beans and ½ cup of water in a bowl. Pour the mixture into the pan. Cover and simmer for 30-40 minutes at low heat. Add a little more water if needed.
Season with salt, pepper, more barbecue sauce and (if using) smoked paprika, to taste.
Serve with barbecued chicken or ribs and coleslaw. Also delicious on toast with eggs and bacon.