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 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 blended.
04 - Add the dry ingredients to the wet mixture and stir gently just until combined. Avoid overmixing to maintain tenderness.
05 - Fold in the diced apples and chopped walnuts or pecans, if desired.
06 - Divide the batter evenly between the prepared muffin cups, filling each about three-quarters full.
07 - Bake in the preheated oven for 18 to 22 minutes, or until a toothpick inserted into the center comes out clean.
08 - Let muffins cool in the pan for 5 minutes, then transfer to a wire rack to cool completely before serving.