Preheat your oven to 350°F (175°C). Line your muffin tin with paper liners or lightly grease each cup with coconut oil to prevent sticking.
In a large bowl, whisk together the oat flour, baking powder, baking soda, salt, and sugar to ensure even distribution.
In a separate bowl, combine the melted coconut oil, Greek yogurt, eggs, and vanilla extract. Whisk until smooth and well incorporated.
Pour the wet mixture into the dry ingredients. Gently fold together with a spatula until just combined to keep the muffins tender.
If using, fold in the chopped chocolate pieces evenly through the batter for delightful pockets of sweetness.
Spoon the batter into the prepared muffin tin, filling each cup about 3/4 full.
Bake for 18-22 minutes, or until a toothpick inserted into the center comes out clean or with just a few moist crumbs. Tops should be golden and spring back lightly when touched.
Let the muffins cool in the pan for 5 minutes before transferring to a wire rack. Enjoy warm or at room temperature.