Preheat oven to 400 degrees F. Line muffin tins with paper or foil cups.
For the Topping
In a small bowl, combine 1/4 cup oats, 1/4 tsp. pumpkin spice or cinnamon, 1 Tbsp. brown sugar, and 1 Tbsp. melted butter; set aside.
For the Muffins
Mash bananas in a medium bowl. Stir in egg and buttermilk.
In a large bowl combine the flour, baking soda, baking powder, salt and remaining amounts of oats, brown sugar and pumpkin spice. Pour the banana mixture into the dry ingredients and stir just to combine. The batter should be lumpy. Stir in raisins.
Divide batter among the prepared muffin cups and sprinkle each with the reserved topping. Bake at 400 degrees for about 20 minutes. Muffins are done when a toothpick inserted in one of the center muffins comes out clean or only with some dry crumbs from the topping.
Tip: Use an ice cream scooper for an easy way to fill muffin cups.