Preheat your oven to 350°F (175°C) and line a muffin tin with paper liners.
In a large bowl, whisk together the flour, baking powder, baking soda, cinnamon, nutmeg, ginger, and salt.
In another bowl, beat the sugar, vegetable oil, eggs, and vanilla extract until well combined.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Fold in the grated carrots and zucchini, and if using, the chopped walnuts and raisins.
Divide the batter evenly among the muffin cups, filling each about ¾ full.
Bake for 20-25 minutes, or until a toothpick inserted into the center comes out clean.
Let the muffins cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.
For the glaze, whisk together the powdered sugar, milk, and vanilla extract until smooth.
Drizzle the glaze over the cooled muffins.
