Add one cup of oats to a blender and blend them into oat flour. Leave the other one cup of oats whole.
Add the rolled oats, oat flour, baking powder, baking soda, cinnamon, nutmeg, salt, and sweetener to a large bowl. After that, thoroughly mix these dry ingredients.
Crack the eggs into a separate large bowl. Then, add the 0-fat Greek yogurt, unsweetened applesauce, vanilla extract, and milk. Whisk these wet ingredients.
Pour the wet ingredients into the bowl with the dry ingredients a little at a time, until fully combined, avoid over-mixing the batter. *Some sugar substitutes absorb more liquid, so if the batter is too dry, add another tablespoon of milk at a time as needed.
Peel and core the apples. Then, evenly chop them into small pieces. Next, gently fold the peeled and chopped apples into the muffin batter.
Spray a non-stick silicone muffin pan with oil or line a muffin tin with parchment muffin liners. After that, use a large ice cream scoop to pour the batter into the muffin pan, forming 10-12 muffins.
Bake the muffins at 350°F for 18-22 minutes, or until a toothpick inserted in the center of a muffin comes out clean. Then, let the muffins slightly cool and enjoy!