Preheat your oven to 350 degrees F and line a baking sheet with parchment paper.
In a large bowl, combine the sugar cookie mix, flour, butter, egg, and lemon zest until a soft dough forms.
Roll the dough into 1-tablespoon-sized balls and place them on the prepared baking sheet, spacing them about 1 1/2 inches apart.
Refrigerate the cookie balls for 30 minutes. You may be tempted to skip this step, but don't, as it prevents the cookies from spreading too much during baking.
Bake the cookies in the preheated oven for 8-10 minutes, or until the edges are lightly golden.
While the cookies are still warm, use the back of a 1/2 teaspoon-sized measuring spoon to make an indentation in the center of each cookie. Allow the cookies to cool on the baking sheet for 5 minutes.
Fill each indentation with a small amount of lemon curd, being careful not to overfill.
Transfer the cookies to a wire rack to cool completely.
In a small bowl, mix the powdered sugar and lemon juice until smooth. Adjust the consistency by adding more lemon juice or powdered sugar if needed.
Once the cookies are completely cool, drizzle the lemon glaze over the top using a spoon or a piping bag.
Allow the glaze to set before serving.