In a mixing bowl, beat eggs, sugar, oil, orange juice and extract. Combine dry ingredients; add to the egg mixture and mix well. Add zucchini and mix well.
Fill greased or paper-lined muffin cups two-thirds full. Bake at 350° for 20-25 minutes or until cupcakes test done. Cool for 10 minutes before removing to a wire rack.
For frosting, combine brown sugar, butter and milk in a saucepan; bring to a boil over medium heat. Cook and stir for 2 minutes. Remove from the heat; stir in vanilla. Cool to lukewarm.
Gradually beat in confectioners' sugar until frosting reaches spreading consistency. Frost cupcakes. Makes 24 cupcakes.