Combine the diced apples, 1/2 cup brown sugar, and raisins in a small sauce pan, and just cover these ingredients with water. Cook for about five minutes. Remove from stove, and add two tblsps butter to melt. Set aside to cool while mixing the rest of the ingredients after adding the butter to melt while it's still hot.
Combine the flour, baking powder, baking soda, salt, cinnamon, oatmeal, and walnuts. Stir in the cooled apple/raisin mixture, remaining brown sugar, oil, and eggs. Mix everything together until just moistened. Bake in a 10 inch bundt pan for about 40 minutes at 350 degrees.
Cool for about ten minutes before removing from pan. The cake may be served warm or cold. You can sprinkle cake with powdered sugar while still warm, or pour a caramel frosting over it. The frosting from the Queen Elizabeth cake within these pages would be delicious with this cake.