01 - Preheat the oven to 375°F. Line a 12-cup muffin tin with paper liners or coat lightly with oil spray.
02 - In a large mixing bowl, whisk together the Greek yogurt, eggs, honey or maple syrup, olive oil or melted coconut oil, and vanilla extract until smooth and fully blended.
03 - In a separate bowl, stir together the whole wheat flour, baking powder, baking soda, ground cinnamon, and salt until evenly combined.
04 - Add the dry mixture into the wet mixture and stir gently just until combined to avoid overmixing.
05 - Gently fold the diced apples and chopped nuts, if using, into the batter until just incorporated.
06 - Divide the batter evenly among 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 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.