Prepare the salted rim by running a lime wedge around the glass. Place the glass upside down in chili lime sea salt mixture.
Add tequila and agave nectar to the cocktail shaker with lots of ice. Shake for at least 20 seconds to mix and chill.
Fill the cocktail glass with crushed ice and the cocktail mixture. Garnish with lime, cilantro, and jalapeño slices.