Step 1

Bring a large saucepan of salted water to the boil. Add the penne, stir once, bring back to the boil, then simmer for 10 minutes, or cook according to packet instructions, until al dente. Drain, then tip the pasta back into the saucepan.

Step 2

Meanwhile, make the cheese sauce. Put the butter in a jug and microwave on high (based on a 900W oven) for 40 seconds, until melted and hot. Stir in the flour to make a paste, then very gradually stir in the milk – this will prevent any lumps forming. Microwave on high for 3-31/2 minutes, stirring every minute, until the sauce has thickened. (Alternatively, melt the butter in a pan over a medium heat, stir in the flour and cook for 1 minute. Gradually add the milk and cook, stirring, for 6-8 minutes until the sauce has thickened.) Stir in 60g Cheddar and season to taste.

Step 3

Preheat the grill to high. Stir the cheese sauce into the pasta, along with the courgette and spinach and mix together to wilt the spinach. Gently mix in the tuna, then tip into a shallow, 2-litre ovenproof dish. Sprinkle with the remaining cheese. Place directly under the hot grill for 5 minutes, until piping hot and the cheese is turning golden.

Step 4

Serve with a green salad.