PREHEAT oven to 350ºF. Grease a bundt pan with oil.
WHISK eggs, water, oil, vanilla extract, zest and cinnamon in a large bowl.
ADD the mix to the wet ingredients and stir until completely combined.
POUR half of the mixture into the prepared bundt cake pan.
SCATTER the apples and walnuts on top and cover with the remaining batter.
POUR into the prepared bundt cake pan.
BAKE for 40-45 minutes or until a toothpick comes out clean.
LET the cake cool for a couple minutes and then carefully flip the cake upside onto a baking sheet to finish cooling.
GARNISH with powdered sugar or all-natural caramel sauce, if desired.
To Toast Walnuts:
PREHEAT oven to 350ºF.
ARRANGE walnuts on a baking dish and bake for 5 minutes or until fragrant.