01 - Preheat the oven to 350°F. Lightly grease a nonstick donut pan to prevent sticking.
02 - In a large mixing bowl, whisk together the mashed bananas, milk, eggs, vegetable oil, granulated sugar, and vanilla extract until the mixture is smooth and well-blended.
03 - In a separate bowl, sift together all-purpose flour, baking powder, baking soda, ground cinnamon, and salt.
04 - Gently fold the dry mixture into the wet mixture, stirring just until combined. Do not overmix to preserve a tender crumb.
05 - Transfer batter into a piping bag or a large resealable plastic bag with the corner cut off. Pipe the batter into the prepared donut pan, filling each cavity about three-quarters full.
06 - Bake for 12 to 15 minutes until the donuts are golden and the tops spring back when gently pressed.
07 - Remove the pan from the oven. Allow donuts to rest in the pan for 5 minutes before transferring to a wire rack to cool completely.
08 - For the glaze, whisk together powdered sugar, milk, and vanilla extract until smooth. Dip the cooled donuts into the glaze and set aside for several minutes for the glaze to set.