Preheat oven to 350 degrees. Coat a muffin pan with cooking spray with flour, see shopping tip.
In an electric mixer or large bowl using a hand mixer, add the cake mix, flour, apple juice, oats, water, applesauce, canola oil, vanilla and cinnamon. Mix until blended. Add the egg whites, egg, and beat until smooth. Stir in the apples. Refrigerate for at least 1 hour to thicken batter and allow apples to blend in. Stir before using. Make sure apples get in each muffin. You might need to add some by hand.
Pour batter into the muffin pan. Fill each almost to top. Spread evenly.
To make crumb topping: In a small bowl add oats, sugar, cinnamon and mix together with a fork. Gradually add melted butter and stir to coat well. Top each muffin with about 1 tablespoon oat mixture.
Bake for 30-35 minutes until a toothpick inserted comes out clean. Remove from oven and cool for about 10 minutes. Carefully loosen each muffin with a knife and remove onto a plate.
Store the muffins covered on the kitchen counter for several days. They freeze great too!