Preheat the oven: Preheat your oven to 350°F (175°C) and lightly grease a small cake pan or line it with parchment paper.

Prepare the batter: In a blender or food processor, pulse the oats until they resemble coarse flour. In a large mixing bowl, combine the ground oats, baking soda, baking powder, and cinnamon. In a separate bowl, whisk together the eggs, honey, yogurt, melted butter (or coconut oil), and vanilla extract until smooth.

Add the apple: Fold the chopped apple into the wet mixture. Then, gradually add the dry ingredients to the wet ingredients, stirring gently until everything is well combined.

Bake: Transfer the batter to the prepared cake pan and smooth it out evenly. Bake for 25 to 30 minutes, or until a toothpick inserted in the center comes out clean.

Cool and serve: Let the cake cool in the pan for several minutes before moving it to a wire rack. It can be enjoyed warm or stored in an airtight container for later use.