Prep. Preheat the oven to 350 degrees. Add non-stick spray to an 8 x 4-inch loaf pan.
Mix. Add the whole wheat flour, baking soda, cinnamon, and salt to a bowl. Whisk.
Whisk. Use a different bowl and whisk the oil, applesauce, milk, egg, sugar, and vanilla.
Make a well. Create a well in the middle of the dry ingredients, and pour in the wet ingredients. Stir by hand to combine (this will be thick and lumpy).
Add the apples. Fold in the prepared apples using a rubber spatula.
Transfer. Put the bread batter into the loaf pan. Pat the top flat with the spatula to level it out.
Make the topping. Add the cinnamon and sugar in a small bowl and sprinkle on top of the bread batter.
Bake. Put the loaf pan in the oven and bake for 25 minutes. Cover loosely with foil, and bake for an additional 20 minutes.
Cool. Place the bread pan on a wire rack and let the bread cool for 10 minutes. Turn the loaf onto the wire rack to finish cooling.