Preheat oven to 400 degrees F (200 degrees C). Spray a 12 cup muffin pan with cooking spray.
In a large bowl, whisk together the 3/4 cup all-purpose flour, 3/4 cup whole wheat flour, 3/4 cup sweetener, salt, baking powder, and 2 teaspoons cinnamon. In a separate bowl, mix 1/3 cup applesauce, egg, and milk. Stir the applesauce mixture into the flour mixture until just blended. Fold in the apples. Spoon into the prepared muffin cups, filling about 2/3 full.
In a small bowl, mix 1/2 cup sweetener, 2 2/3 tablespoons all-purpose flour, 2 2/3 tablespoons whole wheat flour, 1/2 cup applesauce, 1 1/2 teaspoons cinnamon, and oats. Spread evenly over the muffin batter.
Bake 25 minutes in the preheated oven, or until a toothpick inserted in the center of a muffin comes out clean.
