Mix the mustard and honey together with some seasoning. Put the sausages into a foiled-lined roasting tin large enough for there to be a little room around them (too big a tin and the juices will boil off and burn, too small and the sausages will sit in a pool of liquid and won’t go lovely and glossy).
Pour the honey mixture over the sausages to coat, then roast for 25 minutes, turning every so often. They should look burnished.
Cut the cucumber into wafer-thin slices.Mix the soy sauce, vinegar, sugar and chilli in a bowl and stir to help the sugar dissolve. Toss the cucumber into the bowl along with spring onions and sesame oil.
Make the mayonnaise by mixing the mayonnaise, gochujang, garlic and lime together.
Turn the heat down to 150C/140C fan/gas mark 2 and put the hot dog rolls in the oven to warm.
Split the rolls along their length, unless they’re already split. Spread with the spiced mayonnaise then add a sausage to each one. Add the cucumber and lettuce – and kimchi if using – and sprinkle with sesame seeds. Serve immediately.