Make the Cake: Preheat the oven to 350. Lightly grease a 8" round pan that is at least 2" deep.
In a mixing bowl, combine oil and sugar. Stir in sourdough starter. Mix in eggs, one at a time, mixing well after each addition. Fold in pineapple, carrots, walnuts, coconut and vanilla extract.
In a separate bowl, combine flour, ground cinnamon, salt and baking soda. Add the dry ingredients to wet ingredients, stirring until the ingredients are just combined.
Spoon the batter into the prepared pan. Bake for 30~35 minutes or until a cake tester inserted into the center of the cake comes out clean.
Remove cake from the oven and cool completely on a wire rack before frosting.
Make the Cream Cheese Frosting: Beat butter, cream cheese and vanilla extract until light and fluffy. Add the confectioner's sugar gradually until well combined. Add milk, if needed, to get to spreadable consistency.
Frost the cake and sprinkle the chopped nuts.