Preheat oven to 350 degrees. In a blender or food processor, combine chickpeas and eggs until smooth. Add pumpkin, Splenda, syrup, baking powder and spice; process again until smooth.
Spray a round cake pan with oil. Fill with batter. Bake until a knife inserted in the middle comes out clean, about 60 minutes. Cool. (Be sure the cake is completely cool before removing it from the pan, because it is very soft.)
Combine cream cheese and powdered sugar. Spread over top and sides of cake. Decorate with mandarin oranges and walnuts.
