In a medium bowl, combine mashed banana, pudding mix, vanilla bean paste, and sugar.
Whisk in the milk and heavy cream until smooth and fully blended.
Pour the mixture into a Ninja Creami pint container and freeze for 24 hours until completely solid.
After freezing, insert the container into the Ninja Creami, lock into place, and spin on the 'Lite Ice Cream' setting.
Once spun, if the texture is crumbly, respin once more.
Create a small well in the center and add the crushed Nilla Wafers, then select the 'Mix-In' setting.
Serve immediately for soft-serve texture or refreeze for a firmer scoop.