Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking pan or line it with parchment paper.
Grate the zucchini and gently squeeze out excess moisture using a clean towel or paper towels.
In a large bowl, whisk together flour, both sugars, baking soda, baking powder, cinnamon, nutmeg, and salt.
In another bowl, beat the eggs, then add oil and vanilla. Stir in the grated zucchini.
Combine the wet ingredients with the dry ingredients until just mixed. Fold in nuts and raisins or chocolate chips if using.
Pour the batter into the prepared pan and smooth the top.
Bake for 35–40 minutes, or until a toothpick inserted in the center comes out clean.
Cool in the pan for 10–15 minutes before transferring to a wire rack. Let cool completely before slicing.