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 Greek yogurt, eggs, honey or maple syrup, olive oil or melted coconut oil, and vanilla extract until 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 - Gently fold in diced apples and nuts if using.
06 - Divide batter evenly among the muffin cups, filling each about three-quarters full.
07 - Bake for 18 to 22 minutes, or until a toothpick inserted into the center comes out clean.
08 - Let muffins cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.