In a tall mixing jar or small blender, mash the banana with the peanut butter and vanilla until mostly smooth. A fork works fine if you don't have a blender.
Add the chocolate protein powder and 1/2 cup of the almond milk to the jar. Use an immersion blender or a compact blender to blend until fully combined and no dry powder remains, scraping the sides once.
Pour in the remaining almond milk and blend briefly to loosen the mixture; it should be pourable but not watery. If it seems too thick, add up to 1 tablespoon more milk.
Transfer the blended base into a Ninja Creami pint, leaving a little headspace. Seal the pint and place it flat in the freezer. Freeze at least 8 hours (or overnight) until solid.
When frozen, install the pint in the Ninja Creami and run the Lite Ice Cream program once. The texture should be firm and scoopable.
Remove the pint from the machine and create a small well in the center of the ice cream. Pour in 1 tablespoon of almond milk and sprinkle the chopped peanuts into the well.
Return the pint to the Creami and run the Mix-In cycle to fold the nuts into the ice cream. If the texture is still crumbly or too powdery, add an additional tablespoon of milk and run the Re-Spin cycle once.
Spoon into a bowl or enjoy straight from the pint. Add extra chopped peanuts or a drizzle of peanut butter on top if desired.