In addition to naturally sweet apples, other nourishing ingredients in this cake include Omega-3-rich walnuts, along with a duo of fiber-rich flours: whole-grain buckwheat and brown rice. Cinnamon takes the flavor up a notch, and with no eggs or dairy, this cake is perfect for anyone following a vegan diet. Even better? It's totally acceptable to pair a slice with some protein-rich Greek yogurt and happily declare "Breakfast is served!"
Preheat the oven to 350 degrees F. Grease a 10- or 12-inch cast-iron skillet with oil and set aside.
Combine the flours, baking powder, flax meal, cinnamon, baking soda and salt in a mixing bowl, and stir with a fork or whisk until well combined. Add the maple syrup, sparkling water, vanilla and oil and stir well with a fork to combine.
Grate the apples with a box grater or a food processor with a grater attachment blade. Add the apples and walnuts to the batter and stir to combine.
Spoon the batter into the prepared skillet and spread evenly. Bake until the top is lightly browned, 20 to 30 minutes. Let cool 5 minutes, then slice into 8 wedges and serve.