01 - Preheat oven to 350°F. Lightly grease a nonstick donut pan.
02 - In a large mixing bowl, whisk together mashed bananas, milk, eggs, vegetable oil, granulated sugar, and vanilla extract until the mixture is smooth.
03 - In a separate bowl, sift together all-purpose flour, baking powder, baking soda, ground cinnamon, and salt.
04 - Gently fold the dry ingredients into the wet mixture until just combined, avoiding overmixing.
05 - Transfer batter to a piping bag or resealable plastic bag with the corner cut and pipe into the prepared donut pan, filling each mold about three-quarters full.
06 - Bake for 12 to 15 minutes, or until golden and the tops spring back when lightly pressed.
07 - Remove donuts from oven and allow to cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.
08 - For the glaze, whisk powdered sugar, milk, and vanilla extract until smooth. Dip cooled donuts into the glaze and allow to set before serving.