Preheat the oven to 400°F. Grease a muffin pan. Whisk eggs, coconut oil, almond butter, sugar, and vanilla extract until combined. Stir the mashed bananas in the mixture.
In a separate bowl, stir together oat flour, ground flaxseed and baking powder.
Transfer the wet ingredients to the dry. Mix until they are combined. Don't overmix.
Spoon the batter equally into 12 muffin tins. Top them with walnut pieces or chocolate chips.
Bake at 420˚F for 6 minutes in high heat so they get a nice rise on top and then reduce temperature to 350˚F and bake for another 20 minutes.