Place aquafaba (bean liquid) in a mixer bowl and whip on high until stiff, about 5 minutes.
Mix in banana, sugar, vanilla, and oil until smooth.
Mix in chickpea flour, baking powder, and salt (optional) just until blended.
Stir in walnuts.
Heat a pancake griddle (or large skillet) over medium heat. Spray with nonstick vegetable spray. Pour ½ cup ladles of batter onto griddle and cook until golden brown, then turn and cook on the other side.
Serve with additional banana slices and walnuts, if desired.