In a large mixing bowl, combine eggs, softened margarine, vanilla extract, lemon zest, lemon juice, flour, baking powder, and confectioners' sugar until a smooth dough forms.

Divide the dough into two halves. Fold cocoa powder into one half, kneading until the color deepens.

Divide both the chocolate and vanilla dough into two halves each. Roll out the first half of the chocolate dough on waxed paper into a flat sheet.

Roll out one half of the white dough on the same waxed paper, and place this atop the chocolate dough.

Using the waxed paper, roll both doughs together to form a tight cylinder.

Wrap the logs in waxed paper and refrigerate for several hours.

Repeat the process with the remaining dough halves.

Preheat your oven to 350°F (175°C).

Lightly grease cookie sheets.

Unwrap the chilled logs and slice the cookies ¼ inch thick.

Place the slices on the baking sheets, spaced apart.

Bake for 10 to 15 minutes until the edges are lightly golden.

Cool on a wire rack.