Mix together the flour, sugar, cheese, baking soda, baking powder, and salt; add zucchini and stir to separate the shredded pieces. Set aside.
Stir butter into buttermilk.
Gently whisk the eggs and combine with the buttermilk/butter mixture.
Add the onion and stir to combine.
Pour the buttermilk mixture into the flour mixture and stir to combine. The batter will be very thick.
Pour batter into a greased 9"x5"x3" loaf pan (or 3 mini-loaf pans or 12-cup muffin pan).
Sprinkle with black pepper.
Bake at 350° for 50-55 minutes (20-25 minutes for mini-loaves and 15-17 minutes for muffins) or until toothpick inserted in the center comes out clean.
Notes
This recipe makes a loaf of savory zucchini bread with a mild onion flavor and a hint of Parmesan cheese. It's excellent with soup and elevates a grilled cheese sandwich to another level.