01 - Preheat oven to 375°F. Line a 12-cup muffin tin with paper liners or lightly coat with oil spray.
02 - In a large mixing bowl, whisk Greek yogurt, eggs, honey or maple syrup, olive oil or melted coconut oil, and vanilla extract until smooth and homogeneous.
03 - In a separate medium bowl, combine the whole wheat flour, baking powder, baking soda, ground cinnamon, and salt.
04 - Gently stir dry ingredients into the wet mixture just until combined, taking care not to overmix.
05 - Carefully fold in the diced apples and chopped walnuts or pecans if desired.
06 - Spoon batter evenly into the prepared muffin cups, filling each approximately three-quarters full.
07 - Bake in preheated oven for 18 to 22 minutes until the tops are set and a toothpick inserted into the center comes out clean.
08 - Allow muffins to cool in the tin for 5 minutes, then transfer to a wire rack to cool completely before serving.