Preheat the oven to 375 degrees F (190 degrees C). Grease an 8x8 inch square baking pan.
In a medium bowl, stir together 1/2 cup brown sugar and 1 cup flour. Stir in the melted margarine and vanilla until well blended. Press into the bottom of the prepared pan.
Bake for 15 minutes in the preheated oven. Prepare the filling while the crust bakes. In a medium bowl, beat eggs until light and foamy. Blend together the brown sugar, flour, baking powder and salt; stir into the eggs. Mix in the walnuts and coconut. Pour over the crust and return to the oven.
Bake for 15 more minutes in the preheated oven, until set. When cool, cut into squares. Dust with confectioners' sugar.