Coarsely grate courgettes/zucchini.
With the grated courgette in a colander, press down lightly on the courgette to remove some of the liquid. Have the colander over a bowl or plate to collect the liquid. Alternatively, remove the liquid by placing the grated courgette in a clean tea towel and squeezing gently.
Place the cake ingredients, except for the courgette, into the bowl of a stand mixer.
Fit a beater to your mixer and mix the ingredients for 2 minutes, scraping down half way through mixing. You should have a lovely smooth cake batter.
Remove the bowl from the stand and gently fold in the courgettes.
Pour the cake batter into a prepared tin and then gently level off the mixture with a spoon or spatula.
Bake for 1 hour and 10 minutes at 180°C / 160°C fan / 350 °F / Gas Mark 4. When cooked, your cake should be golden brown and spring back when pressed gently. Test your cake is cooked by inserting a skewer or cake tester into the centre and removing it. The cake is ready if the tester / skewer comes out clean.
Cool for 15 minutes in the tin before turning out onto a cooling rack to cool down completely.
Sieve the icing sugar into a large bowl and mix with 3 tablespoons of lemon juice until nice and smooth. The icing should drop slowly off your spoon. Add extra lemon juice if necessary.
Once completely cooled, horizontally slice your cake in half.
Place the top half of the cake upside down on a board or plate. This means the lemon curd filling and the lemon drizzle icing can be placed on flat smooth surfaces.
Spread lemon curd on the plated cake half and then form a sandwich using the other half of the cake.
Spoon icing onto the top of your cake. Work out from the centre of the cake so the icing drips over the edges.
Optional: Sprinkle lemon zest over the top of your iced cake.