Preheat your oven to 350°F (175°C). Line a muffin tin with paper liners or lightly grease each cup. This helps the muffins release easily and keeps cleanup quick after baking.

Place the ripe bananas in a large mixing bowl. Use a fork to mash them until mostly smooth. Small lumps are perfectly fine and will add extra banana flavor throughout the muffins.

Add the Greek yogurt, vegetable oil, brown sugar, egg, and vanilla extract to the mashed bananas. Whisk everything together until the mixture looks smooth, creamy, and well combined without large streaks.

In a separate bowl, whisk together the flour, baking soda, baking powder, cinnamon, and salt. Mixing the dry ingredients first helps distribute the leavening agents evenly throughout the batter.

Gradually add the dry ingredients to the wet ingredients. Stir gently with a spatula until just combined. Avoid overmixing because too much stirring can make the muffins dense instead of soft.

If using chocolate chips or nuts, fold them into the batter now. Stir gently until evenly distributed. These additions create extra flavor and texture while keeping the muffins moist and delicious.

Spoon the batter into the prepared muffin cups. Fill each cup about three-quarters full. This allows enough room for the muffins to rise nicely while baking in the oven.

Place the muffin tin in the oven and bake for 18 to 20 minutes. The tops should look golden and spring back lightly when touched. A toothpick inserted should come out clean.

Remove the muffins from the oven and let them cool in the pan for five minutes. Transfer them to a cooling rack and allow them to cool completely before storing.