Step 1: Preheat your oven to 375°F (190°C). Line a 12-cup muffin tin with paper liners or grease it thoroughly with non-stick spray.
Step 2: In a large bowl, whisk together the all-purpose flour, granulated sugar, brown sugar, baking soda, baking powder, ground cinnamon, ground nutmeg, and salt. Make sure there are no lumps.
Step 3: In a separate medium bowl, whisk together the eggs, vegetable oil, and vanilla extract until well combined.
Step 4: Pour the wet ingredients into the dry ingredients. Stir gently with a spatula or wooden spoon until just combined. Do not overmix; a few streaks of flour are fine.
Step 5: Gently fold in the grated zucchini until it is evenly distributed throughout the batter. If adding optional chocolate chips or nuts, fold them in now.
Step 6: Divide the batter evenly among the 12 prepared muffin cups, filling each about two-thirds full (or almost to the top for higher domes).
Step 7: Bake for 18-22 minutes, or until a wooden skewer inserted into the center of a muffin comes out clean. The tops should be golden brown and spring back when lightly touched.
Step 8: Let the muffins cool in the tin for 5 minutes before transferring them to a wire rack to cool completely. Serve warm or at room temperature.