Dip the rim of your glass in Tajín until it is covered with your desired amount. Set aside.
Add tequila, cucumber vodka, lime juice, Triple Sec, and cucumber mint syrup a few ice cubes to a cocktail shaker.
Cover and shake vigorously for about 10 seconds.
Give the mix a taste and stir in a teaspoon or two of syrup if desired.
Fill the prepared serving glass with ice. Strain in the margarita mix, garnish with a cucumber slice with a sprig of mint.