In a medium bowl, mix together mashed bananas, oats, chocolate chips flax, protein powder and cocoa powder. Using a rubber spatula works well to really push the wet ingredients into the dry.
Next, use a small metal scoop or tablespoon to scoop out one ball. Almost like you're going to stuff a meatball, form it into a small cup and add in 1 teaspoon of nut butter. Then, carefully cover the nut butter with the oat mixture and roll to form into a ball. Refrigerate until chilled and firm, about 30 minutes or longer.