1. For muffins, heat oven to 350 degrees F. Line twelve 2-1/2-inch muffin-pan cups with cupcake/muffin liners.
2. Process the 2 cups oats in a food processor until fine. Transfer oats to a large bowl; stir in flour, the 1/3 cup sugar, the baking powder, baking soda, salt, 1/2 teaspoon cinnamon and 1/4 teaspoon ginger. Whisk together buttermilk, banana, eggs, 2 tablespoons oil and the vanilla in another bowl. Stir buttermilk mixture into flour mixture just until blended.
3. For topping, stir together 1/4 cup oats, 1 teaspoon sugar, 1/2 teaspoon oil, and 1/4 teaspoon each cinnamon and ginger in a cup until combined.
4. Spoon batter into muffin-pan cups. Sprinkle tops with oat mixture. Bake 20 to 22 minutes, until a toothpick inserted in center of a muffin comes out clean.