01 - Preheat oven to 375°F. Line a 12-cup muffin tin with paper liners or lightly grease with oil spray.
02 - In a large bowl, whisk to combine Greek yogurt, eggs, honey or maple syrup, olive oil or coconut oil, and vanilla extract until mixture is smooth.
03 - In a separate bowl, stir together whole wheat flour, baking powder, baking soda, ground cinnamon, and salt.
04 - Add dry ingredients to the wet mixture and stir gently just until combined; avoid overmixing.
05 - Fold in diced apples and chopped walnuts or pecans if using.
06 - Divide batter evenly among muffin cups, filling each about three-quarters full.
07 - Bake for 18 to 22 minutes or until a toothpick inserted in 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.