In a large bowl, mix together the oats, peanut butter, flax, honey, protein powder, vanilla, and chocolate chips. The mixture will be thick.
Use a 2-tablespoon cookie scoop to scoop the mixture, then use your hands to roll it into balls.
Chill in the fridge for 1 to 2 hours, or until firm.
The protein balls keep well in the fridge for up to a week. They also freeze well.
