Preheat oven to 180 degrees C. Grease a 25cm square baking pan.
In a large mixing bowl resift flour with the baking powder, bicarb soda, salt and 3/4 cup of sugar. In a separate bowl combine the egg substitute and water (2 eggs worth) and mix in sour cream substitute and vanilla.
Pour the 'egg' mixture into the flour mixture and beat until smooth. Spread batter in baking pan. Sprinkle blueberries and/or walnuts over the batter and stir slightly so that they stay in the top layer.
In a small bowl combine the 5 tablespoons sugar, margarine and cinnamon. Mix with a fork until mixture resembles polenta (not smooth). Sprinkle topping over batter.
Bake in preheated oven for 20 to 25 minutes or until a toothpick inserted into the centre of the cake comes out clean. Cool slightly before serving.