Add some of your strawberry infused syrup to a small, shallow plate. Add granulated sugar to another small, shallow plate. Dip rim of your glass into syrup then dip into plate of granulated sugar. Repeat process for the second glass.
In a tall mixing glass, add in sliced strawberries, juice from one lemon, a few basil leaves, and 2 oz of strawberry syrup. Muddle everything together. Pour contents into a cocktail shaker with ice. Shake and pour over glass with ice. Top off each glass with tonic water. Add basil and sliced strawberries for garnish. Enjoy!