Prepare the glass: If desired, run a lime or grapefruit wedge around the rim of the highball glass and dip it in salt.
Fill the glass with ice cubes.
Add the liquids: Pour the tequila, grapefruit juice, lime juice, and agave syrup into the glass.
Stir gently with a bar spoon to combine all ingredients.
Top with ginger ale until the glass is nearly full, about 3-4 ounces.
Stir once more very gently to mix without losing too much carbonation.
Garnish with a wedge of grapefruit or lime on the rim of the glass.
Serve immediately while the drink is cold and bubbly.
Notes
This recipe can be easily modified to suit your taste.For a spicier version, use ginger beer instead of ginger ale.If you prefer a less sweet drink, reduce the agave syrup or use sparkling water with a splash of ginger ale.Make a pitcher version for parties by multiplying the ingredients by the number of servings.Add the ginger ale just before serving to maintain the fizz.Non-alcoholic version: Skip the tequila and add a bit more grapefruit juice and ginger ale.The flavor profile stays pretty similar but without the alcohol.The drink pairs well with Mexican food, grilled dishes, and spicy appetizers.