
Preheat your oven to 200°C (180°C fan/gas mark 6). Season the pork loin generously with salt and black pepper. Heat 2 tbsp of olive oil in an ovenproof skillet over medium-high heat. Sear the pork loin on all sides until golden brown, about 4-5 minutes per side.
Add the garlic cloves and rosemary sprigs to the skillet. Transfer the skillet to the preheated oven and roast the pork loin for 15-20 minutes, or until the internal temperature reaches 70°C. Allow it to rest for 10 minutes before slicing thinly.
While the pork is roasting, prepare the pickled onions. Thinly slice the red onion and place in a small saucepan with white wine vinegar, caster sugar, and the bay leaf. Bring to a simmer over medium heat, stirring until the sugar dissolves, then remove from heat and let cool completely.
Slice the ciabatta rolls in half and spread each side with butter. Toast the rolls in a hot pan until golden and crisp, about 2-3 minutes per side.
Assemble the sandwiches by spreading a layer of wholegrain mustard on the bottom halves of the ciabatta rolls. Layer with sliced pork loin, pickled onions, and a handful of rocket. Top with the other half of the roll and serve immediately.
