Heat your oven to 140°C/Fan 120°C/Gas 1. Unwrap the pork and pat it dry with kitchen paper. With a sharp knife, carefully score the skin on top of the pork, cutting about ½ cm deep. Generously sprinkle over sea salt and pepper and rub into all of the grooves.
Pop the joint onto a roasting tin and slide into the oven. Roast for about 1 hr 45 mins, or till the meat is soft and tender.
While the pork belly is cooking, pickle the shallots. Peel and finely slice the shallots and put them in a bowl. Season with salt and pepper. Zest the lemon and set the zest aside. Squeeze the juice from half the lemon over the shallots and toss so they’re well coated in the juice. Cover and set aside.
Raise the oven temperature to 220°C/Fan 200°C/Gas 7. Roast the pork for another 15 mins, or till the crackling starts to bubble and crisp up. Remove from the oven and leave somewhere warm to rest for about 20 mins.
Roughly chop the parsley and garlic. Mix the parsley, garlic, lemon zest and the juice from the remaining lemon half in a bowl. Season to taste and mix with 1 tbsp olive oil.
Slice the rested meat, scatter over the pickled shallots and dollops on the green sauce to serve.