Place the peeled cucumber slices, mint, cilantro and sugar in a cocktail shaker and muddle. Add the lime juice and gin. Fill the shaker halfway with ice and shake vigorously for 1 to 2 minutes (this seems like a long time, but it's essential).
Fill a cocktail glass with fresh ice. Strain the drink into the glass, top with the club soda and garnish with a cucumber slice.
Photograph by John Kernick
Courtesy of Food Network Magazine