Heat oven to 200C/180C fan/gas 6. Half-fill a large pan with water and bring to the boil. Add the potatoes and return to the boil. Cook for 1 min, then drain in a colander and tip into a bowl. Pour over the olive oil, sprinkle with the rosemary and season. Toss together.
Scatter the potatoes over a large baking tray and cook for 5 mins. Turn the potatoes, add the peppers and cook for a further 10 mins or until just beginning to soften. Set aside to cool.
Thread a chunk of yellow pepper, a chunk of potato and a chunk of red pepper onto bamboo skewers, finishing with a piece of chorizo. Place on a parchment-lined baking tray, cover and chill (up to 8 hrs). To make the dip, mix all the ingredients in a bowl, cover and chill.
When ready to serve, heat oven to 200C/180C fan/gas 6. Bake the skewers for 10 mins or until the vegetables are softened and nicely browned, and the chorizo slices are cooked through. Serve with the dip.