Preheat oven to 300 degrees F (150 degrees C). Prepare 2 loaf pans (8 1/2x4 1/2-inch loaf pans) with cooking spray.
Mix flour, baking soda, salt, walnuts, and apples in a large bowl. Whisk oil, sugar, eggs, and cinnamon together in a small bowl; add to flour mixture and mix until just moistened. Evenly divide mixture between prepared loaf pans.
Bake in preheated oven until a toothpick inserted into the center comes out clean, about 90 minutes. Cool in the pans for 10 minutes before removing to cool completely on a wire rack.