To cook the onions, place a cast-iron pan on the hot barbecue and add the oil. When it is hot, add the onions with a generous pinch of salt. Stir well and cook for about 20 minutes until softened, dark and caramelised.
Meanwhile, prepare the sausages. Poke a metal skewer through the length of each sausage and lay the skewers on a tray. Season with the curry powder, trying to get an even coating all over the sausages. Wrap each one in bacon, using 3 rashers per sausage, and secure the bacon with a couple of cocktail sticks.
Lay the bacon-wrapped sausages on the hot barbecue and cook for about 10 minutes, turning every minute or two. While they are on the barbecue, mix the German mustard mayo ingredients together in a bowl, seasoning with salt and pepper to taste; set aside until needed.
Once the sausages are cooked through, lift them off the barbecue and place on a tray. Remove the cocktail sticks and metal skewers.
To build the hot dogs, cut the rolls through the middle and spoon in plenty of caramelised onions. Add the bacon-wrapped sausages and top with the pickle slices and cheese. Place the hot dogs on a sturdy baking tray on the barbecue, put the lid on and leave for a minute or two so that the cheese becomes all gooey and melted.
Transfer the hot dogs to plates and spoon on the German mayo. Scatter over the spring onions for freshness and serve.