01 - Preheat oven to 350°F. Lightly grease a nonstick donut pan to ensure easy release.
02 - In a large 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 to evenly distribute the leavening agents.
04 - Gently fold the dry ingredients into the wet mixture, mixing until just combined. Avoid overmixing to maintain a tender crumb.
05 - Transfer the batter to a piping bag or a resealable plastic bag with the corner snipped. Pipe batter into the prepared donut pan, filling each mold about three-quarters full.
06 - Bake for 12 to 15 minutes, or until donuts are golden and tops spring back when gently pressed.
07 - Allow to cool in the pan for 5 minutes, then transfer to a wire rack and let cool completely.
08 - In a small bowl, whisk powdered sugar, milk, and vanilla extract until smooth. Dip cooled donuts into the glaze and let set before serving.