Preheat oven to 350F degrees.Spray two 9x5-inch loaf pans with non-stick cooking spray. In a bowl, combine the flour, baking powder, baking soda, salt, and cinnamon; set aside. In a large, separate bowl, combine the eggs, buttermilk, and melted butter. Stir in the brown sugar. Add the zucchini, carrots, and apple and combine.Stir in the dry ingredients into the wet ingredients and stir gently until just combined. Pour batter into prepared loaf pans. Bake for 60 minutes, or until a knife inserted into the center of the loaf comes out clean. Cool loaves in the pan for 10 minutes before removing to a wire rack to cool completely.