Preheat oven to 350 degrees F.
In a medium bowl, mix together the all-purpose and whole-wheat flours, the baking powder and salt.
In a large bowl beat together the sugar, honey, eggs, oil, zest, lemon juice and vanilla extract till they are smooth. In batches add the dry ingredients until the mixture forms a dough.
Transfer the dough to a floured surface and knead well. Shape into a log about 10 inches long and 3 inches wide. Transfer to a parchment lined baking sheet and bake for 25 minutes. Take it out and cool for 15 minutes.
With a serrated knife, cut 1/2-inch diagonal slices. Arrange on the baking sheet and bake 10 minutes. Turn the biscotti over and bake for another 10 minutes.
Melt the chocolate in the microwave for 4 minutes, let it cool for 2 minutes and apply a thick layer over the biscotti.
You can store these for 2 weeks.