In a blender, combine the diced dragon fruit and 1 cup of water. Blend until smooth. Strain the mixture through a fine mesh sieve into a bowl to remove the pulp, pressing down with a spoon to extract as much juice as possible. Discard the pulp.

In a large pitcher, combine the fresh lemon juice and granulated sugar. Stir until the sugar is fully dissolved.

Add the dragon fruit juice to the pitcher along with the remaining 3 cups of water. Stir well to combine.

Chill the lemonade in the refrigerator for at least 1 hour before serving.

To serve, fill glasses with ice cubes and pour the dragon fruit lemonade over the ice. Garnish with lemon slices and mint leaves.