01 - Preheat the oven to 375°F. Line a 12-cup muffin tin with paper liners or lightly grease with oil spray.
02 - In a large mixing bowl, whisk together Greek yogurt, eggs, honey or maple syrup, olive oil or melted coconut oil, and vanilla extract until smooth.
03 - In a separate medium bowl, stir together whole wheat flour, baking powder, baking soda, ground cinnamon, and salt until well combined.
04 - Add the dry ingredients to the wet ingredients and mix gently until just combined, avoiding overmixing.
05 - Gently fold in diced apples and chopped walnuts or pecans if using.
06 - Divide the batter evenly among the muffin cups, filling each about three-quarters full.
07 - Bake for 18 to 22 minutes, or until a toothpick inserted in the center of a muffin comes out clean.
08 - Allow muffins to cool in the tin for 5 minutes before transferring to a wire rack to cool completely.