Mix 2 cups flour with 1/4 cup sugar. Blend in butter until finely mixed. Press into a jelly roll pan. Bake 15 minutes at 350 degrees. Beat together eggs, brown sugar, 1/4 cup flour and baking powder. Stir in coconut and nuts. Spread filling over crust and return pan to oven. Bake 25 minutes more. Blend lemon juice, zest, and powdered sugar until smooth. Spread on hot cookies. Cool and cut into bars.