In a large bowl, cream the margarine and sugar together until smooth. Add the vanilla, and the cornstarch/soymilk mixture, and beat until well-mixed.
In a smaller bowl combine the flour, baking powder, salt, and tapioca/corn starch. Stir this into the wet ingredients and combine well.
In a very small bowl stir together the granulated sugar, cinnamon and cocoa powder (if desired).
Begin rolling the cookie dough into balls of about 3 tbsp each. Roll each ball in the cinnamon/sugar/cocoa powder mixture until completely coated and place on an ungreased baking sheet. Continue until all the dough is used up. Using the bottom of a glass, press down on each ball until they are about an inch thick. Bake for 12 - 14 minutes, and no more. The cookies should still seem very soft when you remove them from the oven. Let cool on the pans for about 10 minutes, and then transfer to a wire baking rack and let cool completely.