Preheat oven to 350°F. Grease a 9x5-inch loaf pan and line with parchment paper, leaving overhang for easy removal. Grate zucchini on the large holes of a box grater, then wrap in a clean kitchen towel and squeeze firmly to remove excess moisture. You want about 1.5 cups firmly packed, fairly dry zucchini.

In a large bowl, whisk together the squeezed zucchini, mashed banana, eggs, melted butter, and vanilla until well combined. The mixture will look slightly curdled from the zucchini - this is normal.

In a separate bowl, whisk together almond flour, sweetener, baking powder, cinnamon, and salt, breaking up any almond flour clumps. Add to the wet ingredients and stir with a spatula until just combined with no dry streaks remaining. Do not overmix.

Toss blueberries with 1 teaspoon almond flour, then gently fold into the batter. This helps them distribute evenly rather than sinking to the bottom. The batter will be thick but pourable.

Transfer batter to the prepared pan and smooth the top. Bake 55-65 minutes, until the top is deep golden brown and a toothpick inserted in the center comes out with just a few moist crumbs. The internal temperature should reach 200-205°F. If the top browns too quickly, tent loosely with foil after 40 minutes.

Cool in the pan for 15 minutes, then lift out using the parchment overhang and transfer to a wire rack to cool completely, at least 1 hour. The bread slices much cleaner when fully cooled. Store covered at room temperature for 2 days or refrigerate for up to 5 days.