Combine sugar, water, and lemon zest in a small saucepan. Bring to a simmer until sugar dissolves, steep 20 minutes, strain, and chill.

Cut cucumbers into chunks, purée in a blender, and strain through a fine mesh sieve to yield 1 1/2 cups cucumber juice.

In a large pitcher, combine cucumber juice, fresh lemon juice, and Lemon Simple Syrup. Refrigerate until well chilled.

Just before serving, add sparkling water and ice, stir gently, and pour into tall glasses garnished with cucumber ribbons, lemon wheels, and mint.