01 - Preheat oven to 350°F. Lightly coat a nonstick donut pan with cooking spray.
02 - In a large mixing bowl, whisk together mashed bananas, milk, eggs, vegetable oil, granulated sugar, and vanilla extract until the mixture is fully blended.
03 - In a separate bowl, sift together all-purpose flour, baking powder, baking soda, ground cinnamon, and salt.
04 - Gradually add the sifted dry ingredients into the wet mixture, folding gently until just combined to avoid overmixing.
05 - Transfer batter into a piping bag or zip-top bag with the corner snipped. Pipe batter evenly into the prepared donut pan, filling each cavity about three-quarters full.
06 - Bake for 12 to 15 minutes, or until donuts are golden and tops spring back when lightly touched.
07 - Remove the pan from the oven. Allow donuts to cool in the pan for five minutes, then gently transfer to a wire rack to cool completely.
08 - For the glaze, whisk together powdered sugar, milk, and vanilla extract in a bowl until smooth. Dip cooled donuts into the glaze and set aside until glaze firms, about five minutes.