Blend 4-5 pieces of cucumber with 1-2 shots of Havana rum (any rum can be used, but Havava makes it authentic, Zaya is very good rum)
Muddle a handful of mint with 1 Tablespoon of sugar and juice from 1/2 a juicy lime (roll the line before cutting it in half to get more juice from it)
Combine, add lots of ice and some club soda.
Sem people like more lime, but I like a strong cucumber taste. Adjust to your liking and add a rum float if you want more rum.