Preheat your oven to 350°F (175°C) and prepare a 9x5-inch bread pan by spraying with non-stick spray.

Grate the medium-sized zucchini, wrap in a paper towel, and squeeze out excess moisture.

In a large bowl, combine flour, baking powder, baking soda, and salt. Whisk until well blended.

In another bowl, mix milk and vinegar to create buttermilk. Whisk in melted butter and egg until smooth.

Pour the wet ingredients into the dry ingredients and stir gently until just combined.

Fold in zucchini, cheddar cheese, and green onions until evenly distributed.

Transfer the batter into the prepared pan and smooth the top with a spatula.

Bake for about 1 hour, or until a toothpick comes out clean.

Let cool in the pan for 10 minutes before transferring to a wire rack to cool completely.