Position rack in center of oven and preheat the oven to 350º F.
Grease a 6 by 9-inch loaf pan with the butter and set aside.
In a large bowl, whisk the eggs until yellow and frothy.
Add the vegetable oil, vanilla extract, and sugar and whisk to combine.
Add the zucchini and mix well.
Sift together the flour, cinnamon, baking soda, salt, and baking powder into a medium bowl.
Add the dry ingredients to the wet ingredients and, using a rubber spatula, mix just until blended, being careful not to overmix. Fold in the nuts, if desired.
Pour into the prepared loaf pan and bake until risen and golden brown, about 1 1/2 hours. A toothpick inserted into the middle should come out clean.
Using oven mitts or pot holders, remove the loaf pan from the oven and let cool in the pan for 10 minutes. Turn the bread out onto a wire rack, setting it right side up, to cool completely before cutting.
YIELD: 1 large loaf or 2 small loaves, serving 10 to 12
The bread may also be baked in two small loaf pans. Decrease the cooking time to about 1 hour.