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