Tzaziki: the drink, not the sauce
Just a guess, too, but I've at least seen a drink that could be the one you're looking for: "Munich Mule", a variation on the "Moscow Mule" (http://en.wikipedia.org/wiki/Moscow_mule) where you just exchange the lime for strips of cucumber. I only found recipes in German - obviously invented in Munich, saw it in Berlin once - here is a translation from http://www.rezeptewiki.org/wiki/Munich_Mule:


4 cl Vodka
5 Strips of Cucumber
Ginger Beer
crushed ice


Put the cucumber into a highball glass, add the Vodka. Stir, add the ice and fill with Ginger Beer. Serve immediately.

There also seem to be recipes around that recommend Tonic Water, but I've never seen Mint mentioned.