Preheat the oven to 375 degrees F. Grease a 12-cup muffin pan with nonstick spray.
In medium bowl, stir together the banana, yogurt, butter, eggs, and vanilla.
Add in the flour, cinnamon, if using, baking powder, baking soda, and salt. Gently stir to combine into a thick batter.
Divide batter among the prepared muffin tin, using a heaping 1/4 cup batter in each. (I use an ice cream scoop to make this easy.)
Bake for 14-16 minutes, or until the edges are lightly golden brown and a cake tester inserted into the center comes out cleanly.
Remove from oven, then transfer muffins to a wire rack to cool fully.
Notes
Once cooled, store in an airtight container for up to 3 days at room temperature. Store in the fridge in an airtight container for up to 5 days. Warm slightly to serve from the fridge (they firm up a bit when they're cold so warming slightly returns them to their softer texture).
You can also freeze the muffins in a freezer bag with as much air removed as possible for up to 6 months. Thaw at room temperature or in 15-second increments in the microwave.
Add 1/4 cup sugar to the batter to enhance the sweetness of the muffins if desired.
Add 1/3 cup mini chocolate chips, blueberries, or chopped walnuts to the batter, or sprinkle a little on top of each muffin if desired.
Dairy-free: Use a nondairy Greek style yogurt like the plant-based options from Siggi's and a neutral oil like canola in place of the butter.
Gluten-free: Substitute an all-purpose gluten-free flour in place of the wheat flour.