Combine the tequila, lime zest, lime juice, orange juice and a few ice cubes in a cocktail shaker and shake for 10 seconds. Pour into a rocks glass over ice. Taste, and stir in some simple syrup if you'd like it sweeter. Top off with the ginger beer and garnish with a lime wedge.
To make simple syrup, bring equal parts sugar and water to a boil in a small saucepan, stirring until the sugar dissolves. Cool and chill.