In the meantime prepare the tzatziki sauce for the lamb souvlaki. Pour in a blender the olive oil and grated garlic and blend until combined. Remove the skin and the seeds of the cucumber and grate it into a large bowl. Season with salt and pepper and leave aside for 10 minutes. Wrap the grated cucumber in a towel and squeeze, in order to get rid of the excess water. In a bowl, add the cucumber, the blended garlic and oil, the yogurt, 1-2 tbsps of red wine vinegar, a pinch of salt and blend, until the ingredients are combined. Store the tzatziki sauce in the fridge and always serve cold.