For the syrup, combine water, sugar and ginger in a saucepan over medium heat. Cook mixture over medium heat, stirring constantly until the sugar has dissolved and mixture has thickened. This could take 30-45 minutes. Strain mixture through a fine mesh strainer and allow syrup to cool completely.
In a cocktail shaker, combine syrup, triple sec, tequila, apple cider and ice. Shake for 30 seconds.
Combine sugar and cinnamon on a plate. Dip the rims of two glasses in a splash of water followed by the cinnamon sugar mixture. Pour margaritas into each glass and garnish with apple slices.