Lightly oil your waffle iron, then turn it on to begin preheating.
Whisk the flour, cornstarch, baking powder, cinnamon, and salt together in a large mixing bowl.
Place the bananas into a separate large mixing bowl, then mash them up with a fork or potato masher.
Stir the milk, oil, and vanilla extract in with the bananas.
Begin adding the flour mixture to the banana mixture, mixing in about a third at a time and stirring just until the ingredients are fully combined.
Pour the batter into your waffle iron cavities. Refer to the waffle iron instructions for guidance on how much batter to use (Note 1). Cook the waffles until your waffle iron's indicator light signals they’re done, or until steam has mostly stopped escaping.
Remove the waffles from the iron as they cook, placing them on a cooling rack as they come out. Continue cooking waffles in this manner, adding oil to the waffle iron if needed (Note 2).
Serve topped with vegan butter, maple syrup, and/or fresh banana slices.