Position a rack in centre of oven and preheat to 150°C (130°C fan-forced). Using a sharp knife or box cutter, deepen scoring in the skin and fat of pork (don’t cut through meat). Season the pork generously with salt.
In the centre of a rimmed baking tray, add shallots, garlic and ginger. Top with pork. Roast the pork for 2-2½ hours or until an instant-read meat thermometer inserted in centre of pork registers 50°C. Pour off fat from the tray, then remove excess fat on the tray with paper towel.
Increase oven temperature to 250°C (230°C fan-forced). Roast the pork for a further 20-30 mins or until the skin is crisp and crackling and the internal temperature is 60°C. Transfer the pork to a carving board. Rest for 20 mins.
Meanwhile, to make the chilli-mustard sauce, heat a cast-iron skillet or large heavy-based saucepan over medium-high heat. Add the shallot and cook for 4 mins. Add garlic and chillies and cook, turning, for 6 mins or until charred all over. Transfer to a blender.
Add the sugar, mustard, vinegar, fish sauce, ginger, ground coriander, cumin, ¼ cup (60ml) lime juice and 1 tsp sea salt flakes to the vegetables in blender. Blend until the mixture is completely smooth, stopping the machine and scraping sides as needed. Add basil and coriander leaves and stems and blend until completely smooth. Season with more salt and lime juice, if needed.
To make the herb salad, in a medium bowl, combine the basil, coriander, spring onions, carrot and radishes.
Using a large serrated knife, cut the pork into 2cm-thick slices. Serve pork with the chilli-mustard sauce and herb salad.