Preheat your oven to 350°F (175°C) and line a muffin tin with paper liners or grease it lightly.
In a large bowl, mix together the almond flour, protein powder, baking powder, baking soda, and salt until well combined.
In another bowl, whisk together the Greek yogurt, applesauce, honey (or maple syrup), egg whites, and vanilla extract until smooth. Gradually add the wet ingredients to the dry ingredients, mixing until just combined. If using, gently fold in the mixed berries.
Divide the batter evenly among the muffin cups, filling each about 3/4 full. Bake for 20-25 minutes, or until a toothpick inserted into the center comes out clean.
Allow the muffins to cool in the tin for 5 minutes before transferring them to a wire rack to cool completely.