Cook the pasta in a large pan of boiling salted water for 8 mins until al dente. Drain and tip back into the pan.
Meanwhile heat a large heatproof frying pan and add the mince and some seasoning. Fry for 5 mins, stirring to release the oil and juices until browned all over.
Finely chop the onion and peel and crush 1 clove of garlic. Add to the beef and cook for 10 mins, stirring, until softened
Crush the fennel in a pestle and mortar then add to the pan, stirring briefly. Add the cherry tomatoes - rinse out the tin with a splash of cold water (about 1/4 tin) and add this too. Stir together then simmer, uncovered, for 15 mins.
Preheat the grill. Toss the beef mix into the pasta then tip back into the frying pan or a heatproof dish. Tear over the mozzarella then put until the grill for 5 mins until golden and bubbling.
Meanwhile peel the remaining garlic clove. Zest and juice half the lemon. Whiz together in a food processor with half the rocket and a good pinch of sea salt. Drizzle over the bubbling bake and serve with the remaining rocket.