Preheat the oven to 350°F (180°C). Grease and line a 9x5-inch (23x13 cm) loaf pan with parchment paper.
Grate the zucchini and gently squeeze it with paper towels or a clean kitchen towel. Don't remove all the moisture, just enough so it isn't dripping wet.
In a large bowl, whisk together the flour, baking powder, baking soda, salt, pepper, garlic powder, and Italian seasoning.
Stir in the grated cheddar and Parmesan until everything is evenly coated with flour.
Add chopped chives or green onion and mix to combine.
In another bowl, whisk together the eggs with olive oil or melted butter.
Add buttermilk, and Dijon mustard.
Stir in the grated zucchini until well combined.
Add the dry ingredients and fold gently with a spatula just until no dry flour remains.
Do not overmix.
Transfer the batter to the prepared loaf pan and smooth the top.
Sprinkle with grated cheddar, Parmesan, and chili flakes on top if desired.
Bake for 60-70 minutes, or until the loaf is deeply golden and a toothpick inserted into the center comes out clean.
Let cool in the pan for 10-15 minutes, then transfer to a wire rack to cool for at least 30 minutes before slicing.