1. Preheat oven to 375 degrees.
2. For the Streusel: Mix oats, cinnamon and sugar together. Cut the butter into small pieces and add to the oats. Using your fingers or a pastry blender, rub the butter and flour together until all combined. It will look like small clumps, a bit of loose flour is o.k. Place streusel in the refrigerator while you prepare the muffin batter.
3. Beat together the butter and applesauce until combined. Add egg and egg whites one at a time until well combined, scraping down the bowl in between. In a separate bowl, blend together the flour, protein powder, baking soda, baking powder and salt. Combine the cider, yogurt and vanilla together.
4. Add the flour mixture and cider mixture to the egg mixture alternately starting and ending with the flour. Be careful not to over mix or your muffins will be tough. Gently stir in the shredded apple insides.
5. Scoop batter into greased or lined muffin tin. Divide leftover apple peel and streusel between the muffins and gently press down to adhere. Bake for ~20 minutes or until toothpick inserted in the middle of the muffin comes out clean.