Put a large frying pan on a medium-high heat. Add 1 tbsp olive oil, the beef mince and a pinch of salt and pepper. Use a wooden spoon to break up any lumps and fry the beef for 5-6 mins, stirring occasionally, till it's browned all over.

Meanwhile, fill and boil your kettle. Peel and finely chop the onion. Peel and crush or grate the garlic. When the beef is browned, add the onion and garlic to the pan with 2 tbsp cold water. Fry, stirring often, for 8-10 mins till the onion is glossy and starting to soften.

Fill a large pan with hot water from the kettle and add a good pinch of salt. Cover, set on a high heat and bring to the boil. When the water is boiling, add the penne and simmer for 10-12 mins till the pasta is tender but still has a little bite. Drain and set aside.

Add 2 tsp fennel seeds and 1 tsp dried oregano to the beef. Tip in the tinned cherry tomatoes and add 100ml water. Stir well to mix. Pop a lid on the pan (or use a baking tray if you don't have a lid) and simmer for 15 mins. Stir occasionally and gently crush the cherry tomatoes with the back of the spoon. The sauce should thicken a little as it cooks. If it reduces too quickly, add a splash more water and turn the heat down.

Preheat the grill. Taste the beef sauce and add a pinch more salt or pepper if needed. If your frying pan is roomy enough, and ovenproof, tip in the pasta and stir to mix. If not, tip the pasta into an ovenproof dish, then pour over the beef sauce and fold to mix. Drain the mozzarella and tear it over the pasta. Slide the gratin under the grill for 5 mins till golden and bubbling.

While the gratin grills, toss the rocket with 1 tbsp balsamic vinegar and a little salt and pepper. Serve the gratin on warm plates with the rocket salad on the side.