Preheat the oven to 350°F.

Spray a 9x5-inch loaf pan with nonstick cooking spray. Set aside.

Press the shredded zucchini between two layers of paper towels to remove any excess moisture. Place the zucchini, canola oil, brown sugar, granulated sugar, sour cream, eggs, and vanilla in a large mixing bowl. Whisk vigorously until smooth and combined.

Add the flour, cinnamon, nutmeg (if using), baking powder, baking soda, and salt to the bowl. Continue whisking until the mixture is just combined. Do not overmix. Fold in the raisins and walnuts (if using).

Pour the batter into the prepared loaf pan.

Bake the bread on middle rack of oven until a toothpick inserted in the center comes out clean, 55-65 minutes.

Check to see that bread is done. Remove from oven or add time as needed.

Allow bread to rest in the pan for 10 minutes, then release onto a wire baking rack. Allow to cool for at least 1 hour before slicing and serving. Leftover bread may be stored in a large zip-top plastic bag at room temperature for 1 day, in refrigerator up to 4 days, or in freezer up to 3 months.