Add all ingredients except soda water into a shaker and dry-shake (no ice) to emulsify.
Add ice and shake again until well-chilled.
Double-strain into a Collins glass without ice and top with soda water.
Garnish with a dehydrated or fresh lime wheel.
*Cucumber syrup: Add 1/2 cup sugar and 1/2 cup water into small saucepan and cook on medium heat until sugar is dissolved. Remove mixture from heat, let cool slightly, then add 6 peeled slices of cucumber (1/2-inch-thick each). Allow to steep for 10 minutes, remove solids and store in refrigerator for up to a week.