Make the cinnamon simple syrup by simmering ½ cup sugar, ½ cup water, and 2 cinnamon sticks for 5 minutes. Let cool, then strain.
In a cocktail shaker, combine pear nectar, vodka, cinnamon syrup, and lemon juice with ice. Shake well.
Strain into two glasses filled with ice.
Top with prosecco and a splash of club soda.
Garnish with pear slices and a cinnamon stick.