In a cocktail shaker, add the cucumber slices, basil leaves, and simple syrup. Muddle everything together gently to release the fresh flavors.
Pour the vodka into the shaker.
Fill the shaker with ice and shake well until the drink is chilled.
Strain the cocktail into a glass filled with fresh ice.
Top with 2–3 ounces of prosecco and gently stir.
Serve immediately and garnish with extra cucumber slices or basil leaves if desired.