Start by adding the lemon zest, 1/2 of the sweetener, and 1 cup water to a small saucepan. Bring to a boil over medium high heat, stirring, until the sweetener dissolves. Pour into a bowl that is heat-safe. Let cool.
Meanwhile, make the strawberry syrup. In the same small saucepan, combine strawberries, water, and the other 1/2 of the sweetener, and bring to a boil. Reduce heat; simmer, uncovered for 3-5 minutes or until berries are soft enough to mash. Place strawberries in a strainer, and mash over a bowl, to remove strawberry pulp from strawberry sauce. Let cool to room temperature.
In a pitcher, combine the lemon juice, lemon water, salt, 2 cups cold water, and the strawberry syrup. Fill glasses with ice, pour lemonade into glasses, and top with lemon slices and strawberries if desired!