Preheat & Prep: Preheat your oven to 375°F (190°C). Line a 12-cup muffin tin with paper liners or grease it well.
Mix Wet Ingredients: In a large bowl, mash the ripe bananas with a fork until mostly smooth. Whisk in the egg, maple syrup, Greek yogurt, melted coconut oil, and vanilla extract until fully combined.
Add Dry Ingredients: Add the oat flour, rolled oats, baking soda, cinnamon, and salt to the wet ingredients in the same bowl. Stir with a rubber spatula until just combined. Do not overmix; a few lumps are okay.
Fold in Add-ins: If using, gently fold in the chocolate chips.
Fill Muffin Tin: Divide the batter evenly among the 12 muffin cups, filling each about 3/4 full. If desired, you can sprinkle a few extra oats or chocolate chips on top.
Bake: Bake for 18-22 minutes, or until the tops are golden brown and a toothpick inserted into the center of a muffin comes out clean.
Cool: Let the muffins cool in the tin for 5-10 minutes before transferring them to a wire rack to cool completely.