Preheat oven to 400°F. Line a standard 12-cup muffin tin with paper liners or spray with cooking spray.
In a medium bowl, combine the flours, flaxseed meal, powdered peanut butter, baking soda, xantham gum, and salt.
In a mixing bowl (or the bowl of a stand mixer) mash the bananas (a stand mixer will mash them for you.) Add the brown sugar, peanut butter, coconut oil, and vanilla extract and mix well. Add the egg and beat just until incorporated. Add the flour mixture and beat until combined. Scoop the batter into the muffin tin, dividing equally.
Bake the muffins about 18 to 20 minutes, until a tester inserted into the middle of one comes out clean. Cool the muffins on a rack.