Prepare quinoa according to directions on package. While quinoa is cooking, cut apple in half. Cut one half into thin slices; dice the other half.
Add 1 cup cooked quinoa to a medium mixing bowl with diced apple and all other ingredients (set aside half of the apple you cut into slices). Stir batter until well combined.
Pour batter into a greased 6.5" cast iron skillet. Arrange the sliced apples (from the other half of your apple) on top of the cake and sprinkle with cinnamon.
Bake at 350° for 40-45 minutes. Allow to cool before serving.
Notes
Note: Nutrition information is a rough estimate only; actual values will vary based on the exact ingredients used and amount of recipe prepared.