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.