If you enjoy a salted glass, prep the rim of your glasses by rubbing a lime wedge along the rim. Dip in tequila salt, and set aside.
Make the marg:
Place the diced strawberries and the simple syrup inside a cocktail shaker. Use a muddler to smash them until all the berries have released all their juices and it resembles a strawberry paste.
Add the tequila, triple sec or Cointreau, lime juice, and a handful of ice. Shake vigorously until the sides are fully frosted.
Serve:
Fill the two prepared glasses with ice. Strain the strawberry margarita through the strainer and pour it into the prepared glasses. Top off with sparkling water, to make it a taller cocktail. Garnish with a fresh strawberry and lime wedge.