01 - Preheat the oven to 350°F. Line a 12-cup muffin tin with paper liners or lightly grease each cup with oil or cooking spray.
02 - In a large bowl, whisk together almond flour, coconut flour, baking powder, baking soda, and salt until thoroughly blended and no lumps remain.
03 - In a separate medium bowl, whisk the Greek yogurt, eggs, honey or maple syrup, melted coconut oil or butter, and vanilla extract until smooth and uniform.
04 - Pour the wet mixture into the dry ingredients. Using a spatula, fold gently until just combined—be careful not to overmix as this can make the muffins dense.
05 - Gently fold in the blueberries and lemon zest (if using) until evenly distributed throughout the batter.
06 - Divide the batter evenly among the 12 prepared muffin cups. The cups will be quite full, which is normal for this recipe.
07 - Bake for 22 to 26 minutes, until the tops are golden brown and a toothpick inserted into the center of a muffin comes out clean.
08 - Let the muffins cool in the tin for 5 minutes before transferring them to a wire rack to cool completely.