Mix together the oats, yoghurt, grated apple, granulated sweetener, cinnamon, and vanilla.
Place your mixture in the bottom of a 350ml jar.
In a clean bowl, mix together the "custard" ingredients –fat-free natural yoghurt, quark, vanilla extract, chia seeds, and granulated sweetener. Make sure to beat it well to remove any lumps.
Pour this mixture on top of the oat mixture, close the lid, and refrigerate overnight.