Preheat the oven to 375 degrees. Line a 12-cup muffin pan with baking liners. In a small bowl, mix 1/4 cup sugar with 1 teaspoon cinnamon.
In a large bowl, whisk together the flour, remaining 1/2 cup sugar, baking powder, salt, remaining 1/2 teaspoon cinnamon, walnuts and raisins.
In a small bowl, beat together the banana, yogurt and egg with a fork. Stir in the butter. Stir the wet ingredients into the flour mixture until just combined.
Fill the lined muffin cups with the batter. Sprinkle the reserved cinnamon-sugar mixture on top. Bake until golden and a toothpick inserted into the centers comes out dry, about 20 minutes.