Preheat your oven to 350°F and lightly grease a mini-muffin tin with coconut oil or non-stick spray.
Grate the half apple using a box grater, leaving the skin on for extra fiber, and set it aside.
In a medium mixing bowl, whisk together the rolled oats, vanilla protein powder, ground cinnamon, baking powder, and sea salt.
In a separate smaller bowl, beat the egg and then whisk in the non-fat Greek yogurt and vanilla extract until the mixture is smooth.
Pour the wet ingredients into the dry ingredients and add the grated apple, folding everything together until a thick, uniform batter forms.
Divide the batter evenly into the prepared muffin tin, filling each cup nearly to the top.
Bake for 12 to 15 minutes, or until the bites are firm to the touch and a toothpick inserted into the center comes out clean.
Allow the bites to cool in the tin for 5 minutes before transferring them to a wire rack to cool completely.