01 - Preheat oven to 375°F. Line a 12-cup muffin tin with paper liners or lightly grease each cup 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 well blended.
03 - In a separate medium bowl, stir together whole wheat flour, baking powder, baking soda, ground cinnamon, and salt until thoroughly combined.
04 - Add the dry ingredients to the wet mixture and gently mix just until incorporated, avoiding overmixing the batter.
05 - Fold in the diced apples and, if desired, chopped walnuts or pecans until evenly distributed.
06 - Divide the batter evenly among the prepared muffin cups, filling each about three-quarters full. Bake for 18 to 22 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
07 - Allow muffins to cool in the pan for 5 minutes, then transfer to a wire rack to cool completely before serving.