For the Muffins: Preheat oven to 350ºF and spray 12 muffin cups with nonstick spray or line with paper liners. In a large bowl, combine the flour, sugar, baking powder, and salt. In another bowl, add the milk, egg, applesauce, orange juice, vanilla, and zest and mix until combined. Add the milk mixture to the flour mixture and stir until just combined, then stir in the chocolate chips. Fill the muffin cups about ¾ full and bake at 350ºF for 22-25 minutes. Allow muffins to cool for 10 minutes, then drizzle with glaze (see recipe below).For the Glaze: Combine the confectioners' sugar, orange juice, and zest in a small bowl and stir until completely smooth. Spoon glaze over the cooled muffins.