Preheat oven to 350°F. Lightly coat two cookie sheets with cooking spray; set aside.
In a large bowl, stir together banana, peanut butter, honey, and vanilla.
In a small bowl, combine oats, flour, ground flax, protein powder, cinnamon, and baking soda.
Stir the oat mixture into the banana mixture until combined. Stir in raisins.
Using a ¼-cup measuring cup, drop mounds of dough 3 inches apart on prepared cookie sheets. With a thin metal or small plastic spatula dipped in water, flatten and spread each mound of dough to a 2 ¾-inch round, about ½ inch thick.
Bake, one sheet at a time, for 14 to 16 minutes or until browned. Transfer to wire racks to cool completely.
Store in an airtight container or resealable plastic bag for up to 3 days or freeze for up to 2 months; thaw before serving.
Notes
Make sure to use old-fashioned oats (not quick or instant) for this recipe. Using quick/instant oats will make the cookies lose their shape.
Make this recipe gluten-free by using a 1:1 gluten-free all-purpose baking flour.
You may substitute the ground flaxseed (flax meal) for the same amount of flour.
If your mixture is too thick, add a tablespoon or two of water to the mixture. Some protein powders are thicker than others and they will yield slightly different textures to the dough.