In a mixing bowl, combine rolled oats, peanut butter, honey or maple syrup, and vanilla extract until well blended.
Stir in chocolate chips and ground flaxseed if using.
Use your hands to form the mixture into small balls, about 1 inch in diameter.
Place the cookie dough balls on a baking sheet lined with parchment paper.
Refrigerate the balls for about 30 minutes to set.
Notes
Store in an airtight container in the refrigerator for up to a week or freeze for up to three months. Consume at room temperature or lightly thawed for best flavor.