Preheat oven to 425°F degrees. Line a 12-count muffin pan with muffin liners or spray with nonstick spray. Set aside.
In a medium bowl, mix the mashed bananas, brown sugar, yogurt, egg, milk, peanut butter and vanilla together until smooth..
In a large bowl, whisk together the flour, cinnamon, baking soda, baking powder, salt. Pour the wet ingredients into the dry ingredients and stir until just combined. Do not overmix the batter or you will have tough muffins.
Evenly distribute the batter between the muffin cups. (I use an ice cream scoop for easy portioning). Bake for 5 minutes at 425°F degrees. Keeping the muffins in the oven, reduce the oven temperature to 350°F and continue to bake for another 12 minutes or until a toothpick inserted in the center comes out clean.