Combine oats, peanut butter, honey, chocolate chips, flaxseed, and vanilla in a large bowl and stir until fully mixed.

Refrigerate the mixture for 30 minutes so it firms up and is easier to roll.

Roll into 1-inch balls using your hands and place on a parchment-lined sheet.

Refrigerate for another 15 minutes until set, then store in an airtight container up to one week.