Preheat oven to 350 degrees Fahrenheit.
Combine margarine, flour and sugar and press into a sided jelly-roll pan (baking pan with sides). Bake for 15 minutes, then cool on a wire rack while you prepare the filling.
In a separate bowl, combine eggs, brown sugar, salt, baking powder and vanilla and beat until thick. Add the coconut and nuts.
Spread over the crust and return to the oven for 25-30 minutes.
Combine the confectioner's sugar, lemon zest and enough lemon juice to make a thick but still spoonable icing. Drizzle the icing over the bars while they are still hot, then allow to cool completely. Refrigerate for several hours before cutting into bars.