Combine the water, sugar, cinnamon sticks, and lemon zest in a medium saucepan. Split vanilla bean lengthwise, scrape out the seeds and add both the seeds and the pod to the pan. Bring the mixture to a boil over medium heat, stirring occasionally, until the sugar is completely dissolved, about 5 minutes.
Peel the pears. Reduce the poaching liquid to a simmer and add the pears. Cook until just tender (the tip of a paring knife will go through the flesh of a pear with just a little resistance), about 15 minutes. Remove the pan from the heat and cool the pears in the poaching liquid, until completely cooled, about 45 minutes.
Heat the cream in a small saucepan over low heat. Put the chocolate and butter into a medium-size bowl. Pour the cream over the chocolate and stir until smooth and glossy.
Serve the pears with a scoop of ice cream, a little pear-poaching syrup and warm chocolate sauce drizzled over the top. Garnish with a wafer cookie and serve.