(Nutrition information is calculated using an ingredient database and should be considered an estimate.)
Heat the oven to 160C/140C fan. Grease and line a deep 20cm cake tin. Line a sieve with tea towel or kitchen cloth, tip the grated courgette in and use to squeeze as much moisture out of the mix as possible. Whisk the melted Flora, eggs and 200g of the sugar with an electric whisk until thick and glossy, around 3 mins.
Tip the self-raising flour, lemon zest, baking powder and bicarbonate of soda into the bowl, stir to combine, then add the squeezed courgette and a pinch of salt. Stir well, then tip into the cake tin and bake for 50mins - 1 hour, or until the cake is pulling away from the sides and a skewer comes out clean.
Whilst the cake is baking, make a syrup by heating the juice from two of the lemons with the remaining sugar. Once the cake is baked, cool for 5 mins in the tin, then transfer to a cake rack, flipping the cake upside down so you have a nice flat surface. Use a skewer to poke holes in the cake and brush with the syrup. Leave to cool.
Make the icing. Whisk the mascarpone, Flora, lemon zest and icing sugar with a hand whisk until combined. Use a spatula to spread the icing over the cooled cake. Decorate with lemon zest.