Beat the egg whites with the lemon juice until soft peaks form. Gradually add the powdered sugar and continue beating until stiff and glossy. Fold in the ground hazelnuts and cinnamon.
Transfer the mixture to a piping bag affixed with a large, round tip and pipe 50 small mounds onto a baking sheet lined with parchment paper. Top each mound with a blanched hazelnut and bake in an oven preheated to 150°C (approximately 300°F) for 20-25 minutes, until golden brown.