Preheat oven to 350 degrees F (175 degrees C). Grease and flour one 9x5 inch loaf pan.
In a medium bowl, combine flour, baking soda, baking powder, cinnamon and salt. Set aside.
In a large bowl, cream together butter and brown sugar. Beat in eggs one at a time, then stir in vanilla. Add grated zucchini and walnuts (optional) and mix well.
Add dry ingredients to the zucchini mixture and stir to combine. Pour batter into prepared pan.
In a small bowl, combine 1/2 cup white sugar and 1 teaspoon cinnamon. Sprinkle over batter. Drizzle with melted butter.
Bake for 50 to 60 minutes, or until a toothpick inserted into center of the loaf comes out clean. Cool in pan 10 minutes, then turn out onto a wire rack.
Interesting Facts
Zucchini is a type of summer squash.
Zucchini is a good source of vitamins A and C, potassium, and fiber.
The zucchini should be grated on the large holes of a box grater.
Baked zucchini bread can be stored at room temperature for up to three days.