Stir together cocoa and boiling water until smooth. Set aside to cool to room temp. Place flour, baking soda, baking powder, salt and sugar in mixer bowl and mix at low speed about 1 minute to blend. Add egg substitute, sweetener, and vanilla to cooca mixture and mix well. Add margarine to dry ingredients along with cocoa mixture and mix well at medium speed about 1 minute. Pour into 9" square or 9x13 cake pan that has been greased with margarine.Bake at 350 F for about 30 minutes, or until a cake tester comes out clean and cake pulls away from the sides of the pan. Cool in the pan and cut 6x3 to yield 18 pieces.