Start by stirring some ice cubes in the highball glass with a bar spoon.
Measure and pour ½ oz simple syrup into the shaker.
Add 1 oz fresh lemon juice.
Add 1½ oz mango purée as well.
Finally, add 2 oz Gin to the mix.
Fill a highball glass with ice cubes.
Fill the shaker with ice, close it and give it a good shake (10-15 seconds).
Using the cocktail strainer, strain the mixture from the shaker into the ice filled glass.
Top-up with chilled soda water and stir gently to combine.
Finally, place a lemon slice and/or a mint sprig into the glass for garnish.