Preheat oven to 350 degrees.
In a medium mixing bowl whisk together flour, baking soda, cinnamon, and salt. Set aside.
In a large mixing bowl, beat the banana till completely smooth. Add brown sugar, yogurt, vegetable oil, egg, and vanilla with a mixer until well combined. Add flour mixture and mix again until well incorporated. Using a wooden spoon, stir in muesli.
Drop cookie dough by the spoonful in mounds about 2" apart on parchment paper-lined cookie sheets. Bake for 10 to 11 minutes.
Remove from oven and allow to cool on cookies sheets for a minute or two then transfer to wire racks to cool completely.