Finely slice the courgettes into thin rounds - if you have a mandoline, use this to make the rounds really thin. Quarter the tomatoes.
Arrange the courgette rounds on a large serving plate. Top them with the rocket and tomatoes quarters. Scatter over the basil leaves.
Drain the mozzarella. Tear it into small chunks and scatter it over the salad.
Finely grate the zest from the lemon and sprinkle it over the salad. Juice half the lemon and whisk it with 2 tbsp olive oil and a good pinch of salt and pepper. Taste and adjust the seasoning in the dressing, then drizzle it over the salad. Serve straight away.