Preheat oven to 350 degrees Fahrenheit.

In a large bowl, whisk eggs until they are foamy and pale yellow.

Add the Greek yogurt, coconut sugar, and vanilla to eggs. Whisk until the mixture thickens and is well combined (it will still be a little runny).

Add oats, baking powder, salt, cinnamon, and apple. With a spatula, fold ingredients.

Pour in the milk and continue mixing until everything is well incorporated (it will be a loose mixture).

Using a medium-sized ice cream scoop, scoop the batter into 12 muffin tin cups lined with cupcake liners. Fill cups close to the top as these muffins do not rise too high.

Bake 35 to 40 minutes, until the muffins have set and just started to turn golden brown.