Add all dry ingredients to a large mixing bowl. Mix until combined and there are no lumps. Set aside.
Add the pistachios to a food processor and blitz until it forms medium to fine crumbs. Add the avocado, milk, oil, lemon juice/zest and vanilla. Blitz until there are no more chunks of avocado. The mixture may be lumpy from the pistachios.
Pour the pistachio mixture into the mixing bowl with the flour. Mix gently until combined. The batter needs to be quite thick (otherwise the cake will not bake through).
Pour or scoop the cake batter into your loaf tin.
Bake the cake for 60-70 minutes OR until a skewer can be inserted into the middle and there is no wet batter on it.** If the cake is browning too quickly but is uncooked in the middle, cover the cake with an oven safe bowl or aluminium foil and bake until ready. The cake is very moist and there might be some crumbs on your skewer which is fine.
Allow the cake to rest in the tin for at least 10 minutes. Remove it from the tin and allow it to cool on a wire rack. The cake might deflate which is fine.