Puree the watermelon in a blender until smooth. Keep aside.

Puree the cucumber along with lime juice and sugar until smooth, Place a fine mesh sieve over a bowl and pour both the puree through it, pressing against the sieve with a rubber spatula to extract as much liquid out as possible.

Fill a jug with ice cubes and pour the juice into it. Add mint leaves, and adjust sugar as per your need, stir well.

Serve in glasses and garnish with watermelon slices (optional).