Preheat oven to 350 degrees. Make the cookies: Combine flour, baking powder, and salt in a bowl. Pulse sugar and zest in a food processor until combined, about 2 minutes.
Beat sugar-zest mixture and butter in a mixer on medium speed until pale and fluffy, about 2 minutes. Add eggs, 1 at a time, beating well after each addition. Add vanilla and lemon juice. Reduce speed to low. Gradually add flour mixture, and beat until combined.
Scoop 1 tablespoon dough (or use a 11/8-inch ice cream scoop), and transfer to a lightly floured surface. Roll dough into a 4-inch rope. Bring ends together, overlapping slightly, and press together to form a ring. Repeat with remaining dough. Transfer rings to parchment-lined baking sheets, about 1 1/2 inches apart, as you work. Bake until pale golden on the bottoms and around the edges, about 18 minutes. Transfer to wire racks, and let cool.
Make the glaze: Whisk together confectioners' sugar and lemon juice in a small bowl until smooth. Dip the top side of each cookie into glaze, letting excess drip off. Return cookies to wire racks, glaze side up, and sprinkle with nonpareils. Let dry completely.
Decorated cookies can be stored at room temperature for up to 3 days.