01 - Preheat the 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 smooth.
03 - In a separate bowl, sift together all-purpose flour, baking powder, baking soda, ground cinnamon, and salt.
04 - Fold the dry mixture into the wet ingredients just until combined, taking care not to overmix the batter.
05 - Transfer the batter to a piping bag or resealable plastic bag with a snipped corner and pipe into the prepared donut molds, filling each about three-quarters full.
06 - Bake for 12 to 15 minutes, or until golden and the tops spring back when lightly pressed.
07 - Remove from oven, let donuts cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.
08 - For the glaze, whisk together powdered sugar, milk, and vanilla extract until smooth. Dip each cooled donut into the glaze and set aside until glaze is set.