Crush the fennel seeds lightly in a pestle and mortar. Mix with half the oil and a little seasoning. Rub into the pork and set aside.
Heat oven to 200C/180C fan/gas 6. Heat remaining oil in a shallow ovenproof dish. Soften the onion and garlic for about 5 mins, then tip in the potatoes and brown for a few mins. Add the fennel, lemon juice and about 100ml water. Season, cover with the lid and cook in the oven for 35 mins.
Remove the lid, stir the potatoes and place the meat on top. Return to the oven, uncovered, and cook for another 10 mins or until the pork is cooked to your liking. Meanwhile, cook the broccoli.
Scatter over the reserved fennel fronds and serve with the broccoli.