Into a blender, place the frozen mixed berries, banana, Greek yogurt, skim milk, and vanilla protein powder. Blend until completely smooth, then pour the mixture into a Ninja Creami pint container.

Place the pint container in the freezer for 24 hours, until the mixture is solidly frozen.

Take the frozen pint out of the freezer, hold it under hot water for 60 seconds, and then set it into the Ninja Creami machine. Before spinning, make sure the pint's surface is level; a surface that is not even can harm the blade.

For the initial spin, press the Smoothie Bowl button. Take off the outer bowl lid. If the ice cream remains powdery, put it back in the machine and press the Respin button.

Inspect the ice cream; the finished result should be creamy and smooth in texture. If the consistency you want is not achieved, pour in a little more liquid and spin again using the Respin setting.

Scoop the smoothie bowl into a small bowl and top with your preferred toppings.