In a mixing glass or directly into your rocks glass: add orange pieces, strawberry chunks, basil leaf, and bitters. Muddle these 4 ingredients until crushed and combined.
Now add one or two large cocktail ice cubes to the same glass, and use a jigger to measure and splash in simple syrup plus the bourbon.
Stir everything together with a bar spoon until fruit and bourbon are combined and everything is chilled through: about 30 to 40 seconds.
(Optional) Add a little splash of sparkling water to top it off. Serve ice cold, chilled.