Preheat the oven to 350°F (175°C) and line a muffin tin with paper liners.
In a large bowl, whisk together the mashed bananas, eggs, melted butter, yogurt, brown sugar, and vanilla until well combined.
Sprinkle in the oats and let the mixture sit for 5 minutes. This softens the oats a bit and gives the muffins a better texture.
Add flour, cinnamon, baking soda, and salt. Stir until just combined—don’t overmix.
Scoop the batter evenly into the prepared muffin tin. Fill each about 3/4 full.
Bake for 20–25 minutes or until a toothpick comes out clean. Cool in the tin for 5 minutes, then transfer to a rack.