Preheat the oven to 180℃/350F fan, 200℃/ 400F or Gas Mark 6.
Mix the sugar, oil and eggs until well beaten.
Stir in the grated courgettes (after you've squeezed out the liquid - see recipe tips).
Stir in the nuts (if using), lime zest, self raising flour, bicarbonate of soda and cinnamon. Stir until totally combined.
Pour into a lined and greased loaf tin and bake for 45-60 minutes until cooked through and a skewer comes out clean.
Allow to cool and remove from the tin.
Meanwhile, make the icing by very gently combining the mascarpone with sieved icing sugar and lime juice. Pop into the fridge until the cake is totally cold.
Smooth the icing over the top of the cake and sprinkle on the pistachios and more lime zest if you fancy.
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