Preheat the oven to 200°C fan-forced.
Add the fennel, red onion, cherry tomatoes, cannellini beans and sliced garlic to a large roasting tray.
Sprinkle over the fennel seeds, salt and pepper.
Pour over the olive oil, white wine and white wine vinegar. Toss gently to coat everything.
Nestle the Italian pork and fennel sausages amongst the vegetables and beans. Tuck the rosemary sprigs around the tray.
Roast, uncovered, for 45–55 minutes, turning the sausages and gently stirring the vegetables halfway through, until the sausages are beautifully golden, the fennel is tender and caramelised, and the tomatoes have burst to create a light, flavourful broth.
Remove the rosemary sprigs.
Scatter over the lemon zest, parsley and fennel fronds.
Serve immediately with plenty of crusty bread to soak up the pan juices.