In a medium bowl, combine the sliced strawberries and granulated sugar. Toss gently and let sit for about 15 minutes to allow the strawberries to release their juices.
After 15 minutes, mash the strawberries lightly with a fork or potato masher to create a chunky puree.
In a large pitcher, combine the strawberry puree with the fresh lime juice. Stir well to mix.
Fill glasses with ice cubes and pour the strawberry-lime mixture over the ice, filling each glass about halfway.
Top off each glass with club soda or sparkling water, stirring gently to combine.
Garnish with fresh mint leaves if desired and serve immediately.