Put the sesame seeds in a dry frying pan and toast over a medium-high heat, stirring from time to time, until fragrant; tip out of the pan and set aside.
Meanwhile, mix the vinegar, honey, sesame oil and a large pinch of salt in a bowl and add the carrot; cover and chill in the fridge, allowing the mixture to quick-pickle until ready to serve.
Heat a griddle pan over a medium-high heat and cook the frankfurters for 7-8 minutes, turning regularly, until piping hot throughout. While they’re cooking, mix the mayonnaise and gochujang chilli paste in a small bowl; set aside.
Split open the rolls and spread a little of the spicy mayo inside each one. Lift the carrot from its pickling liquor and arrange in the rolls, then top with the frankfurters. Drizzle over the remaining spicy mayo and sprinkle over the sesame seeds to finish. Serve any leftover carrot on the side.