For the lemon syrupIn a small saucepan, combine the lemon juice, 1/2 cup water, and the sugar over medium heat. Bring to a boil, reduce the heat, and simmer for 5 minutes, stirring occasionally, until the sugar has dissolved. Take the pan off the heat and allow the syrup to cool, about 20 minutes. Stir in the hazelnut liqueur. For the tiramisuIn a food processor or blender, pulse the hazelnuts until finely chopped. Add the lemon zest and pulse once to combine. Set aside. Whip the cream in a large bowl until thick. Add the cinnamon and 2 tablespoons of the sugar and continue to whip until the cream holds soft peaks. In another bowl, beat together the remaining 3 tablespoons sugar and the mascarpone cheese for 30 seconds. Mix one-quarter of the whipped cream into the mascarpone. Using a rubber spatula, fold in the remaining whipped cream. Set aside. Pour the lemon syrup into a small, shallow bowl. Dip 16 of the ladyfinger cookies in the syrup. Line the bottom of a 13 X 9 X 2-inch serving dish or other decorative serving dish with the dipped cookies, trimming the cookies, as necessary, to form an even layer. Spread one-third of the mascarpone mixture over the cookies. Sprinkle with one third of the hazelnut mixture. Form 2 more identical layers, each consisting of 16 dipped ladyfinger cookies and ending with a layer of the mascarpone mixture sprinkled with the hazelnut mixture. Cover and refrigerate for at least 6 hours or preferably overnight. Remove the tiramisu from the refrigerator at least 1 hour before serving.