Preheat the oven (select the hot air fan setting) to 160-170C (340F). In a large mixing bowl, whisk together the oil and the sugar, the lemon juice and the lemon zest, until the mixture reaches a cream like consistency. In a glass, dissolve the baking soda in the water and pour it in the bowl. Be careful to do this while standing over the mixing bowl in order to catch any spill, as the soda froths and rises. Next, add in the mixture the last ingredient, the flour, and mix everything to a homogenous dough.
Roll the dough with your hands into small balls, each the size of a walnut, and place these cookies on the baking tray, making sure that you leave enough space between them, as the cookies will rise.
Mix the mint and sugar in a bowl and put half of a teaspoon of this mixture on top of each cookie dough. Press the dough of each cookie with the spoon so that the sugar mixture sticks to each cookie.
Bake for only 8-10 minutes and no longer, to avoid getting dry and hard cookies.
Take the lemon and mint cookies out of the oven and allow them to cool for few minutes before serving.