Preheat your oven to 350 degrees F and lightly coat a 8x4-inch loaf pan with baking spray. Set aside.
Spread the walnuts in a single layer on an ungreased baking sheet. Place in the oven and bake until toasted and fragrant, about 8 to 12 minutes, stirring once throughout. DO NOT WALK AWAY during the last few minutes and set a timer. Nuts love to burn the very moment you stop watching. Transfer to a cutting board. Once cool enough to handle, roughly chop and set aside.
In a large mixing bowl, combine the white whole wheat flour, baking soda, cinnamon, and salt. In a separate bowl, whisk together the applesauce, canola oil, milk, sugar, egg, and vanilla until smooth.
Make a well in the center of the dry ingredients, then add the wet ingredient all at once. Mix in by hand just until combined. The batter was looking be very thick and stiff. Fold in the apples and walnuts. It will be hard to do because the batter is so thick. Use a rubber spatula and smush and push it around gently but firmly as needed. Distribute the apples and walnuts as evenly as you can.
Pour the batter into the prepared loaf pan. With the back of a rubber spatula, press and smooth the top so it is mostly flat. For the cinnamon sugar topping, stir the cinnamon and coarse sugar together in a small bowl. Sprinkle evenly over the top of the batter.
Bake for 25 minutes, loosely tent with foil, then bake for 20 additional minutes, until a toothpick inserted in the center comes out clean without any wet batter clinging to it (quick breads can be hard to judge; the best way is to take its temperature with an instant read thermometer. When the bread hits 195 to 200 degrees F, it's done). Place on a wire rack and let cool 10 minutes in pan, then turn out onto a wire rack to cool completely. Enjoy warm, at room temperature, and/or smeared with butter, peanut butter, or almond butter.
Store leftover apple bread in an airtight container at room temperature for four days or freeze for up to two months. Let thaw overnight in the refrigerator.