Turn on the oven to 180°C - 350°F Line a square baking pan with baking paper.
In a large mixing bowl beat egg whites until soft peaks form, using the hand electric mixer. Gradually add the sugar and beat until it's well combined. Add oil and continue to beat until it's fluffy and white cream.
Turn off the electric mixer. Sift the flour with the baking powder upon the egg white mixture. Stir gently with the wooden spoon until it's completely combined.
Peel, core and slice the apple. Arrange the fruit slices on the bottom of the prepared baking pan. Sprinkle with all spice. If desired you can now cover the apple with sliced almonds.
Drop batter over the apples.
Bake in the preheated oven about 30-35 min, or until a toothpick insered in the center of the cake comes out clean.
Allow to rest about 10 minutes on a wire rack, then remove from the pan. Slice into squares and dust with confectioners' sugar.