Moisten the rim of a highball glass with a lime wedge and press into the Tajín seasoning until coated.

Add two jalapeño slices and the lime juice to the bottom of the glass; muddle briefly to release capsaicin oils.

Fill the glass completely with ice cubes.

Pour the tequila over the ice.

Top the mixture with chilled Topo Chico sparkling mineral water.

Stir gently with a long bar spoon once or twice to combine without depleting carbonation.

Garnish with the remaining jalapeño slice and a lime wedge.