Preheat the oven to 350°F (175°C). Grease two 9x5-inch loaf pans and line them with parchment paper, leaving a slight overhang on the long sides. This makes lifting the loaves out cleanly after they cool.
In a large mixing bowl, whisk together the mashed bananas, melted butter, yogurt, eggs, brown sugar, granulated sugar, and vanilla extract until smooth. The mixture should look glossy and well-emulsified — no streaks of butter remaining.
In a separate bowl, whisk together the flour, baking soda, baking powder, cinnamon, nutmeg, and salt. Add the dry ingredients to the wet mixture and fold with a rubber spatula until just combined. A few streaks of flour are fine — overmixing at this stage will make the bread tough. You want a tender crumb, not a sturdy one.
Fold in the squeezed-dry shredded zucchini. Take your time here — the zucchini should be evenly distributed through the batter, not clumped in one area.
In a small bowl, toss the blueberries with 1 tablespoon of flour until each berry is lightly coated. This prevents them from sinking to the bottom of the loaf during baking. Gently fold the blueberries into the batter with just a few strokes. Do not overmix or the berries will bleed into the batter and turn it grey.
Divide the batter evenly between the two prepared loaf pans. If using the topping, sprinkle the turbinado sugar and sliced almonds evenly over the top of each loaf.
Bake for 60–75 minutes, rotating the pans halfway through. The bread is done when a toothpick inserted into the center comes out clean or with just a few moist crumbs attached. If the top is browning too quickly before the center is set, tent loosely with foil at the 45-minute mark.
Let the loaves cool in the pans for 15 minutes on a wire rack. Then lift them out using the parchment paper overhang and transfer to the rack to cool completely. This bread cuts cleanly only when fully cooled — resist the temptation. The texture does not finish setting until it reaches room temperature.