Preheat oven to 350 degrees F (175 degrees C). Grease 16 muffin cups or line with paper liners.
Whisk flour, bran, rolled oats, flax seeds, baking powder, baking soda, cinnamon, salt, ginger, allspice, and nutmeg together in a bowl. Mix bananas and peanut oil together in a separate large bowl; stir dry ingredients into banana mixture. Fold walnuts, chocolate chips, and raisins into batter. Spoon batter into prepared muffin cups, filling them about 2/3 full.
Bake muffins in the preheated oven until lightly golden brown and a knife inserted into the center of a muffin comes out clean, about 30 minutes.