Preheat your oven to 350°F (175°C). Line a muffin tin with paper liners or lightly grease it to prevent sticking.
In a large mixing bowl, whisk together the all-purpose flour, baking soda, baking powder, salt, ground cinnamon, and nutmeg.
In another bowl, combine vegetable oil, granulated sugar, and brown sugar. Beat in the eggs one at a time until fully incorporated. Stir in grated zucchini, vanilla extract, lemon zest, and fresh lemon juice.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix; a few lumps are fine.
Spoon the batter into the prepared muffin tin, filling each cup about two-thirds full.
Bake for 18-22 minutes or until a toothpick inserted in the center comes out clean. Muffins should be golden brown and slightly springy.
While baking, prepare the lemon glaze by whisking powdered sugar with a few tablespoons of lemon juice until smooth and pourable. Adjust consistency as needed.
After baking, cool muffins in the pan for 5 minutes, then transfer to a wire rack to cool completely. Drizzle lemon glaze over each muffin and let it soak in.