Set oven to 350 degrees Fahrenheit (175 degrees C).
Combine the onion, zucchini, cheese, oil, eggs, and milk in a big bowl.
Mix the flour, baking soda, salt, and baking powder in a separate bowl. This should be mixed briefly after being added to the wet components.
In a prepared 9x13-inch baking pan, pour the batter. A toothpick put into the center of the bread should come out clean after 35 to 40 minutes of baking.
Before slicing and serving, let the bread cool. Enjoy!