Make flax egg by whisking ground flaxseeds with 3 tablespoons of water until the mixture becomes gelatinous. Allow it to sit for 5 minutes.
Peel and Mash bananas in a medium bowl. Add flaxseed mixture, oil, sugar, vanilla, salt, baking soda and mix well.
Add flour and combine.
Pour the batter into the greased pan. Gently cover the pan with a paper towel. Using a piece of aluminum foil, cover the paper towel and gently secure the paper towel around the rim of the cake pan. Add 1 cup of water to the Instant Pot. Place the cake pan on the trivet. Gently put the trivet in the pot. Close Instant Pot lid with pressure valve to sealing.
Select Manual/Pressure Cook (Hi) and adjust the cook time to 50 minutes. Allow 10 minutes of natural pressure release.
Open the Instant Pot and carefully lift the trivet with the pan, and take it out. Allow the banana bread to cool for 5 minutes and then flip the bread onto a plate.
Use store-bought flaxseed meal or make it at home by grinding whole flax seeds in a coffee grinder.
You can also bake this banana bread in the oven for 50 minutes at 350 degrees.
Sprinkle chocolate chips or rough-chopped walnuts just before cooking.