Preheat your oven to 250°F (120°C) and line baking sheets with parchment paper.

In a food processor, blend the confectioners' sugar, sliced almonds, and ground cinnamon until finely ground.

Whip egg whites in a large bowl until soft peaks form, then gradually add remaining confectioners' sugar, mixing until thick and glossy.

Fold the almond mixture and lemon zest into the whipped egg whites to form a stiff dough.

Roll out the dough to about 1/4-inch thickness and use a star cookie cutter to cut shapes.

Spread a thin layer of the meringue mixture on each star and decorate with additional almond slices.

Bake the cookies in the preheated oven for 30 minutes until the bottoms are light golden brown.

Let the cookies cool in the oven with the door slightly ajar for about 10 minutes.