How to Make It
Combine 3/4 cup water, sugar, fennel, and 5 lemon rind strips in a small saucepan over medium-high heat. Heat 4 minutes or until sugar dissolves, stirring with a whisk. Remove from heat; let stand 15 minutes. Strain mixture through a fine sieve; discard solids.
To prepare each cocktail, combine 3 tablespoons syrup, 1/2 cup cucumber juice, and 1 tablespoon lemon juice in a cocktail shaker; shake 30 seconds. Pour into a glass filled with ice. Top each with 1/3 cup club soda; stir. Garnish each with 1 lemon rind strip.