Preheat the oven to 220C, fan-forced. Line an oven tray with baking paper. Cut the unpeeled potato into matchsticks (see Kitchen hack). Put the potato on the lined tray. Drizzle with 1½ tsp olive oil and 1 tsp white vinegar, season with salt and toss to coat. Bake the fries on the upper shelf for 25-27 mins until tender and golden.
Step 2 — Make coriander sauce
While the fries are baking, finely chop the coriander, including the stems. Combine the coriander, 1½ tbs olive oil and 1 tsp white vinegar in a bowl and season with salt and pepper.
Step 3 — Caramelise onion
Cut the onion into thin wedges. Heat ½ tsp olive oil in a medium frypan over medium heat. Cook the onion, stirring, for 5 mins or until soft. Add half the barbecue seasoning*, 2 tsp sugar, 2 tsp white vinegar and 1 tbs water and cook, stirring, for 2-3 mins until caramelised. Taste, then season with salt and pepper. Remove from the pan and wipe the pan clean.
Step 4 — Cook chorizo
Cook the chorizo in the same pan over medium-high heat, turning, for 4-5 mins until browned. Remove from the pan. Meanwhile halve the rolls through the middle, taking care not to cut all the way through. Put on an oven tray and bake on the lower shelf for 3-4 mins until toasted.
Step 5 — Serve up
Halve the chorizo lengthwise. Spread the rolls with the barbecue sauce and mayonnaise. Fill with the chorizo and caramelised onion, then drizzle with the coriander sauce. Serve with the fries and enjoy!
Step 6 — Kitchen hack
Here's an easy way to cut the potato into matchsticks: thinly slice lengthwise, then stack the slices and cut into matchsticks.