Slice thin rounds of cucumber and place in your cocktail glasses. From the remaining cucumber, cut off 5-6 chunks to muddle into the cocktail, and save the rest.
Squeeze the lime juice into a cocktail shaker and add the gin, St Germain, basil, agave, and cucumber chunks.
3 ounces gin, 2 ounces St. Germain elderflower liqueur, 1 medium lime, 3 sprigs basil, 1 medium cucumber, 2 teaspoon agave nectar
Muddle the ingredients well, and then add ice.
Ice
Shake well, then pour to divide between 2 glasses. Top with tonic and garnish with basil