01 - Preheat oven to 375°F. Line a 12-cup muffin tin with paper liners or lightly coat with oil spray.
02 - In a large mixing bowl, whisk together Greek yogurt, eggs, honey or maple syrup, oil, and vanilla extract until fully combined.
03 - In a separate medium bowl, stir together whole wheat flour, baking powder, baking soda, ground cinnamon, and salt.
04 - Gently add the dry mixture to the wet mixture, stirring just until no streaks of flour remain. Avoid overmixing for tender muffins.
05 - Fold diced apples and chopped nuts (if using) into the batter until evenly distributed.
06 - Evenly divide the batter among the prepared muffin cups, filling each approximately three-quarters full.
07 - Bake in the preheated oven for 18 to 22 minutes or until a toothpick inserted into the center of a muffin emerges clean.
08 - Allow muffins to cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.