Preheat an oven to 180C and grease the bottom of a chiffon/angel food cake tin.
Sift the dry ingredients, except the sugar, into a bowl and then gently whisk together to lighten further.
In another bowl, whisk together the egg yolks, 1 cup of caster sugar, oil and avocado.
Mix this into the dry ingredients and set aside.
Whisk the egg whites until foamy, then slowly add the sugar while whisking to soft peaks. Fold 1/3 of the meringue into the batter to loosen, then gently fold in the remaining meringue.
Spoon into the prepared chiffon cake mould and bake for 35-40 minutes.
Check if the cake is cooked by inserting a skewer. If it comes out clean then flip upside down using the feet on the cake mould stand and cool upside down for 1 hour.
Carefully remove from the tin, using a pallet knife to release it around the edges and place on a flat plate.
Whip the avocado puree, icing sugar and lime juice to a smooth thick icing and spoon that over the cake decorating with pistachios is desired.