01 - Preheat the oven to 350°F. Line a 12-cup muffin tin with paper liners or lightly grease each cup with cooking spray or butter.
02 - In a large mixing bowl, whisk together almond flour, coconut flour, baking powder, baking soda, and salt until thoroughly blended and no lumps remain.
03 - In a separate bowl, whisk the Greek yogurt, eggs, honey or maple syrup, melted coconut oil or butter, and vanilla extract until smooth and emulsified.
04 - Pour the wet ingredients into the dry ingredients. Using a spatula, fold gently until just combined—stop mixing as soon as the flour disappears. The batter will be thick.
05 - Gently fold in the blueberries and lemon zest if using, taking care not to crush the berries. Distribute them evenly throughout the batter.
06 - Divide the batter evenly among the 12 prepared muffin cups. Fill each cup to the top, as the muffins will rise only slightly during baking.
07 - Bake for 22 to 26 minutes, rotating the pan halfway through, until the tops are golden brown and a toothpick inserted into the center comes out clean or with just a few moist crumbs.
08 - Let the muffins cool in the tin for 5 minutes to set. Then carefully transfer them to a wire rack to cool completely before serving.