Mix the quark, milk and oat flakes to a homogeneous mass. If necessary, let the oat flakes soak briefly.
Chop the apple into small pieces (as coarse or fine as you like). Chop the walnuts and mix everything well again. If necessary, sweeten with honey or maple syrup.
The recipe can of course be varied. Any kind of fruit is possible and instead of nuts you can use e.g., also take desiccated coconut. Tastes very tasty and is very filling.