Add gin and the simple syrup to a stemmed wine glass. Add in a few ice cubes and top up with tonic water. Garnish with chopped strawberries and basil leaves.
(Make rhubarb simple syrup by adding chopped fresh rhubarb and strawberries, 3/4 cup raw cane sugar and a cup of water to a saucepan. Bring to boil and simmer 10 minutes until fruit breaks down. Strain this mix and chill in fridge.)