Pat the pork belly dry and score the skin in close parallel lines without cutting the meat.
Preheat the oven to 220°C.
Rub the pork with oil and a mixture of rosemary, fennel seeds, pepper, lemon zest, and salt.
Place pork on a rack in a tin and roast for 40 minutes at 220°C until the skin puffs.
Slice the fennel bulbs into wedges and flatten the garlic cloves.
Lower oven to 160°C and add fennel, garlic, and wine to the tin beneath the pork rack.
Roast for one hour, removing the fennel once it becomes tender and golden.
Squeeze lemon juice over the cooked fennel and keep it warm.
Increase oven to 200°C and cook the pork for 20 minutes until very crisp.
Slice the pork and serve with fennel garnished with reserved fronds.