Preheat oven to 350 F. Grease a 9-inch round cake pan; set aside.
In a medium bowl, whisk together flours, cinnamon, nutmeg, ginger, baking soda, and salt. Set aside.
In a large bowl, whisk together olive oil and sugars.
Add egg, buttermilk, Greek yogurt, and vanilla extract. Whisk in until well-combined.
Whisk in flour mixture until just combined.
Pour salted caramel sauce into the bottom of cake pan.
Arrange apple slices over caramel, and sprinkle nuts over apples.
Carefully pour batter over apple slices.
Set the cake pan on a cookie sheet.
Bake for 30-35, or until a wooden toothpick inserted into the center comes out clean.
Let the cake cool in the pan for 10 minutes.
Loosen and invert onto plate to finish cooling.
Drizzle with additional salted caramel sauce.