Preheat oven to 375 degrees and grease a muffin pan with nonstick cooking spray or add liners.
In a large bowl, whisk together the flour, oats, flax seed, baking powder, and salt. Set aside.
In a separate bowl, beat together the peanut butter, bananas, brown sugar, and sugar.
Add the eggs and vanilla and beat until combined. Mix in the milk.
Add the flour mixture to the peanut butter mixture and mix until combined.
Fold in the chocolate chips.
Fill each muffin cup ¾ of the way full with batter and bake in the preheated oven. Bake for 20 to 25 minutes for full-size muffins or 18 to 22 minutes for mini muffins.
Allow to cool in pan for 5 minutes, then transfer to a wire cooling rack to cool completely before serving.
Notes
The gluten-free version of all our recipes are tested with Bob's Red Mill gluten-free 1-to-1 Baking Flour.Storing the muffinsStore the cooled muffins in an airtight container at room temperature for up to 3 days.