Slice the lemon in half and place one half in a cocktail shaker. Reserve the other half. Add the zested ginger and the 2 cucumber wheels and muddle until the lemon has released its juices and oils. Add the Pimm’s and fill the shaker with ice. Shake until cold, then double-strain into an ice-filled Collins glass. Top with the lemon soda. Make a twist from the reserved lemon half and drape it and the the reserved cucumber wheel over the edge of the glass as garnish.