Sift the flour, baking powder and salt into a medium bowl.
In a separate bowl cream the ½ cup margarine and the cream cheese or sour cream. Add the sugar half a cup at a time. Add the egg replacer and beat well.
Combine the flour with the butter mixture, adding ⅓ of it at a time. Add the vanilla and lemon zest.
Pour the batter into the pan and smooth it with a spatula.
Spread half of the crumb mixture over the batter. Layer the apple slices on top of that, and then cover with the rest of the crumb mixture.
Bake on the center rack for 50 to 60 minutes. Test with a toothpick. (should come out clean) Transfer cake to a rack and cool completely in pan. Slice and serve.