Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x5 inch loaf pan.

In a large bowl, cream together the sugar and softened butter until light and fluffy.

Beat in the eggs one at a time, then stir in the grated zucchini, milk, apple cider vinegar, and vanilla.

In a separate bowl, whisk together the gluten-free rice flour blend, baking soda, and salt.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Pour the batter into the prepared loaf pan.

Bake for 60 minutes, or until a toothpick inserted into the center comes out clean.

Let the bread cool in the pan for 5 minutes before transferring it to a wire rack to cool completely.