Start by preheating the oven to 160C.
In a bowl, mix the pistachios (after first beating them in the blender and keep 1 tbsp for serving), the lemon zest, the flour, the sugar substitute, the baking powder, the salt.
In another bowl, mix the water, the olive oil, 2 tbsp lemon. Pour the liquids into the solids and mix lightly. Do not overdo it with the mixing.
Grease your mold well or put non-stick paper.
Pour in the mixture. Bake for 50-55 minutes. See if your cake is ready by piercing it with a knife. If the knife comes out clean then the cake is ready.
Take it out and let it cool completely before unmolding it. Take it out of the mold and let it cool well before putting the icing on it.
For the icing, mix the icing substitute in a bowl with 3 tbsp lemon juice. See if you need a little more lemon. Pour the icing on your cake and sprinkle with the grated pistachios that you kept. Let it dry for about 30 minutes. Cut and enjoy.