Put the low-fat quark (preferably organic) in a slightly larger bowl and stir in honey or stevia. If the quark is still very firm, add a little water and stir, preferably with a fork, until the quark is creamy. Then add oatmeal, fruit and trail mix and stir in. If the muesli is still very dry, stir in some more water.
You can also make the trail mix yourself, with nuts and unsweetened dried fruits of your choice.