Preheat the oven to 180C/350F/Gas 4.
Place the nuts, flour and salt in the bowl of a food processor and process until the nuts are ground.
Place the egg yolks and sugar in a separate bowl and beat for three minutes, or until the mixture is pale and creamy. Fold through the zest and coconut, then the nut mixture.
Place the egg whites in a clean, dry, stainless steel bowl and whisk until stiff peaks form. Using a large metal spoon, fold lightly through the nut batter.
Spread the batter evenly into a 23cm (9in) greased or non-stick springform cake tin. Bake for 40 minutes, or until the cake is lightly golden.
Meanwhile, make the icing. Combine all the icing ingredients in a bowl and mix until smooth and glossy.
Remove from the oven and leave to sit for 10 minutes in the tin. Turn the cake out onto a serving plate. Spread the lime icing over the warm cake, allowing it to drizzle down the sides.