Mix together eggs, vegetable oil, sugar and vanilla.
Mix in the baking soda, baking powder, salt, flour, and cinnamon. Fold in the zucchini and walnuts.
Spray a 7-inch baking pan with nonstick cooking spray.
Spread the batter into the pan.
Add 1 ½ cups of water to the inner pot of the Instant Pot.
Cover the pan with foil and using either the sling method or a trivet with handles, lower the pan into the instant pot.
Close the lid of the Instant Pot and turn to sealing position.
Set for a manual high-pressure time of 60 minutes. When the time has finished, allow for a natural release.
Cool on the counter for an hour and then run a fork around the edge of the cake if needed to loosen before tipping the cake out of the pan.