To a cocktail shaker, add jalapenos, brine, lime juice, and agave.
Muddle the jalapeños in the shaker with the brine, lime juice, and agave.
Add tequila and Cointreau.
Fill the shaker with ice and shake until well-chilled.
Strain over fresh ice into a glass rimmed with spicy salt.
Garnish with a pickle chip, jalapeño slice, or lime wedge.