01 - Preheat oven to 350°F and lightly grease a nonstick donut pan.
02 - In a large mixing bowl, whisk mashed bananas, milk, eggs, vegetable oil, granulated sugar, and vanilla extract until the mixture becomes smooth.
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 ingredients until just combined. Avoid overmixing the batter.
05 - Transfer the batter into a piping bag or resealable plastic bag with a corner snipped. Pipe the batter into the prepared donut pan, filling each cavity about three-quarters full.
06 - Bake for 12 to 15 minutes until donuts are golden and tops spring back when lightly pressed.
07 - Let donuts cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.
08 - Whisk powdered sugar, milk, and vanilla extract until smooth. Dip each cooled donut in glaze and allow to set for several minutes before serving.