Preheat oven to 375°. In medium bowl mix 1/2 cup brown sugar, 1/2 cup margarine and 1 cup flour with fingertips or fork until crumbly. Pat into 8×12 baking pan, covering bottom, bake 10 minutes. Cool. Meanwhile, mix 1 cup brown sugar, eggs, 2 tablespoons flour, baking powder and vanilla. Beat well. Add coconut and pecans. Pour over crust, spreading over crust evenly. Bake 20 minutes.