Prepare your oven and pan. Preheat oven to 350°F. Lightly grease a 9×5-inch loaf pan and line it with parchment paper, leaving a little overhang along the sides so the bread is easy to lift out after baking. Mix the dry ingredients. In a medium bowl, whisk together the whole wheat pastry flour, all-purpose flour, baking soda, baking powder, cinnamon, nutmeg and salt. Set aside.
Combine the wet ingredients. In a large bowl, whisk the eggs and cane sugar together for about 30 to 60 seconds, until well combined and slightly lighter in color. Add the mashed banana, avocado oil, milk, vanilla extract and lemon juice, whisking until smooth.
Add the zucchini. Gently fold the grated zucchini into the wet ingredients. The zucchini should be lightly squeezed to remove excess liquid, but don't wring it completely dry.
Combine wet and dry ingredients. Add the flour mixture to the wet ingredients and gently fold everything together with a spatula. Mix only until you no longer see streaks of flour. A few small lumps are perfectly fine!
Transfer to the loaf pan. Pour batter into your prepared pan and use a spatula to spread it evenly and smooth the top.
Bake. Bake for 50 to 60 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean. Start checking around the 50-minute mark. If the top begins browning before the center is finished, loosely cover the loaf with aluminum foil.
Cool before slicing. Let the bread cool in the pan for about 10 to 15 minutes before lifting it out using the parchment paper. Transfer to a wire rack and let cool for at least 30 minutes before slicing.