Preheat the oven to 200C/gas 6/fan 180C. Heat half the oil in a non-stick frying pan and cook the onion over a low heat for 5 minutes. Tip into a 20x15cm ovenproof dish. Heat the remaining oil in the pan, add the pork and lightly brown on all sides for 5 minutes, then sit it on top of the onions. Crush together the fennel seeds, sea salt and a grinding of black pepper and sprinkle over the pork.
Bring the stock to the boil, then pour over the pork. Roast in the oven for 15 minutes. Add the beans and roast for another 5-7 minutes, or until the pork is cooked.
Mix the garlic with the lemon zest and parsley. Slice the pork, put on top of the beans and onions and sprinkle with the garlic mixture.