Preheat the oven to 180C/350F/Gas 4.
For the lamb, flatten the meat out with a meat hammer or rolling pin and set aside.
Place the bread, lemon zest, herbs, salt and freshly ground black pepper in a food processor and pulse to breadcrumbs. Tip the mixture out onto a baking sheet.
Dust the lamb with the flour, then dip into the beaten egg and then roll in the crumb mixture, patting gently to secure the crumbs to the meat.
Heat the oil in an ovenproof frying pan and fry the lamb for 2-3 minutes on both sides, or until golden, then transfer to the oven. Cook for 5-6 minutes, or until golden-brown and cooked to your liking.
For the onion jam, melt the butter in a small pan and gently fry the onion with the sugar for 3-4 minutes, or until softened. Add the balsamic vinegar and cook for 4-5 minutes, or until the mixture is thick and sticky.
For the fennel, heat the olive oil in an ovenproof frying pan and fry the fennel with the zest and garlic for 2-3 minutes, then transfer to the oven. Cook for 6-8 minutes, or until the fennel is golden and tender.
Spoon the onion jam onto a serving plate and place the panéed lamb on top. Serve the fennel alongside.