Place the strawberries on a plate and freeze until firm, at least 1 hour.
Meanwhile, bring 1/3 cup water and the sugar to a boil in a small saucepan over medium heat, stirring occasionally, until the sugar dissolves. Let cool completely.
Combine the cooled syrup, strawberries, 1 1/2 cups ice, the lemon juice and gin in a blender. Blend until thick and smooth. Pour into glasses and garnish each with a lemon slice.
Photograph by Levi Brown