To prepare the pork, at least one night before cooking, using a sharp knife or box cutter, gently deepen scoring on rind and extend existing scoring so that all of the rind is scored. Be sure to cut all the way through rind and fat until you reach meat (don’t cut through the meat). Refrigerate pork, uncovered, for at least 12 hours and up to 2 days. Let stand at room temperature for 1 hour before cooking.
Preheat oven to 250°C (230°C fan-forced). Rub salt into scored rind. Season cut side of pork with salt and place on a rack set in a roasting pan.
Roast pork for 30 mins or until rind is crisp and golden. Reduce oven to 160°C (140°C fan-forced) and roast for 2½ hours or until an instant-read thermometer inserted into centre of pork registers 65°C. Transfer pork to carving board to rest for 20 mins.
Meanwhile, prepare a covered barbecue for high heat. On a large baking tray, toss tomatoes, chillies and spring onions with oil and season with salt. Lightly oil barbecue grates, place vegetables on barbecue and close lid. Cook vegetables, turning only once, for 8 mins each side for tomatoes, 6 mins each side for chillies and 3 mins each side for the spring onions or until blackened as much as possible (don’t worry if tomatoes break open and begin to fall apart – it’s a sign that they’re cooked through). Using tongs, transfer vegetables to a baking tray and cool slightly. Trim stems from chillies and remove seeds, if desired (don’t remove charred skin).
In a blender, combine blackened vegetables, garlic, coriander and 2 tbs lemon juice and blend until mostly pureed but still chunky. Season with salt.
Serve pork with salsa, tortillas, cabbage, radishes and avocados.