Mix butter and sugar until creamy. Beat in egg. Add the rest of the dry ingredients and mix well. When you get a dough consistency, mix in the lime peel and chocolate by hand. Press into a 9x9 baking dish that's been sprayed with cooking spray. (I use Baker's Joy!) Bake 20-25 minutes at 350 degrees until they're lightly browned. Cool, then top with the glaze. Once the glaze has hardened, cut into bars.
To make the glaze, combine all the ingredients and mix well.