You'd think that a meat or cheese filled pastry would be a massive hit with Poles.
I remember in Bulgaria once there was a stand selling fresh baked things for locals (one British tourist ahead of me was shooed away like a stray dog when she asked a question in English) I could read the menu well enough to give convincing enough order and it was great, a couple of different baked pastries with various fillings that were filling and delicious (and not as heavy as some Bulgarian food - usually Bulgarian equivalents of Balkan-Greco-Turkish dishes are super heavy).
But then I also like langos and think that could be a food truck type thing here.... I used to have my own rating of the best langos in Budapest (number 1 at the Ecseri flea market, number 2 and Hold utca market... but since closed : (