Confidence: It's likely to be this, but I can't be certain.
Notes: The plant leaves look like those of a Sow Thistle (Sonchus sp.), in which case the most likely cause of the mines is a Chromatomyia species of fly, either Chromatomyia syngenesiae and Chromatomyia horticola. Mines cannot be identified as to species. This can only be done by dissecting male adult flies. The mines are characterised by long twists and turns. It looks as if the early stages are shown here and they should develop to reflect the complex patterns shown here -
As suggested below, best to re-classify under the invertebrate section.