Preheat your oven to 350°F (175°C) and line a 12-cup muffin tin with paper liners or lightly grease with cooking spray.
Combine all dry ingredients in a large bowl: whole wheat flour, rolled oats, baking powder, baking soda, pumpkin pie spice, and salt. Whisk together until well integrated.
Mix the wet ingredients in a separate medium bowl: pumpkin puree, Greek yogurt, brown sugar, maple syrup, eggs, vanilla extract, and oil. Stir until smooth and no large lumps remain.
Pour the wet mixture into the dry ingredients and gently fold together with a spatula just until combined. Do not overmix—a few small lumps are fine and preferable to tough muffins.
Fold in your optional mix-ins of nuts, chocolate chips, or dried fruit if using, with just 2-3 gentle strokes.
Divide the batter evenly among the prepared muffin cups, filling each about ¾ full. For bakery-style muffins, you can sprinkle a few extra oats on top.
Bake for 22-25 minutes or until the tops are golden and a toothpick inserted into the center comes out clean or with just a few moist crumbs.
Cool in the tin for 5 minutes, then transfer muffins to a wire rack to cool completely.