Add the lime juice, tequila, cranberry cocktail juice, ginger liqueur, fresh ginger simple syrup and a handful of ice in a cocktail shaker.
Put the top back on the cocktail shaker. Give it a good, vigorous shake. About 15-30 seconds will take care of the job.
Add ice to the serving glass and strain the margarita into the glass. Top with a splash of ginger beer or ginger ale. If desired, garnish with sugared cranberries. Enjoy!