Preheat your oven to 350°F (175°C). Grease a 9x5-inch loaf pan or line it with parchment paper.
In a large mixing bowl, whisk together the flour, baking powder, salt, black pepper, garlic powder, and cayenne pepper.
In another bowl, combine the grated zucchini, chopped green onions, and shredded cheddar cheese. Stir until the vegetables and cheese are well coated with the flour mixture.
In a separate bowl, beat the egg, then add the milk and vegetable oil. Mix until well combined.
Pour the wet ingredients into the dry ingredients and stir gently until just combined. Do not overmix; a few lumps are okay.
Fold in the zucchini, green onions, and cheese mixture until evenly distributed.
Pour the batter into the prepared loaf pan and smooth the top with a spatula.
Bake in the preheated oven for 50-60 minutes, or until a toothpick inserted into the center comes out clean.
Allow the bread to cool in the pan for 10 minutes, then transfer it to a wire rack to cool completely before slicing.