For the cucumber juice, add 3 tablespoons of water to a blender with a peeled and chopped cucumber, blend into a juice, then strain with a fine mesh strainer. To a cocktail shaker, add one mint sprig and slap it to release oils. Add all other liquid ingredients (mezcal, triple sec, cucumber juice, lime juice, agave) to the shaker and fill with ice. Shake vigorously for 30 seconds. Strain the mixture over fresh ice into a glass. Garnish with a lime zest/salt rim, fresh mint, and a cucumber slice. Serve and enjoy!