On a small plate or in a shallow bowl, stir together the sugar, kosher salt, and lime zest, rubbing the mixture with your fingers to release the lime’s oils. Run a lime wedge around the rim of a rocks glass, then dip or roll the rim in the sugar-salt mixture until evenly coated. Tap off any excess and set the glass aside.
Fill a cocktail shaker halfway with ice. Add the lime juice, mango nectar, tequila, and orange liqueur.
Cover and shake vigorously until the shaker is very cold.
Fill the rimmed glass with fresh ice. Strain the margarita into the prepared glass.
Garnish with a lime wedge, if desired, and serve immediately.