Preheat your oven to 350°F (175°C). Prepare your muffin tin by lining it with paper liners or greasing it.

In a large mixing bowl, combine the dry ingredients: flour, oats, baking powder, baking soda, cinnamon, nutmeg, and salt. Mix well.

In another bowl, whisk together the wet ingredients: pumpkin puree, Greek yogurt, honey or maple syrup, melted coconut oil, and eggs until smooth.

Pour the wet ingredients into the dry ingredients and stir gently until just combined. Fold in chocolate chips or nuts if using.

Divide the batter evenly among the muffin cups, filling each about 2/3 full.

Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted into the center comes out clean. Allow to cool for 5 minutes before transferring to a wire rack.