Preheat oven to 400 degrees F. Line 12-cup muffin pan with paper muffin cups.
In a large bowl, whisk together flour, brown sugar, baking soda, baking powder, nutmeg, cinnamon, and salt until smooth. Stir in oats and raisins. Add oil, egg, milk, carrots, and banana. Stir until blended.
Fill each muffin cup with 1/4 cup batter. Bake until a toothpick comes out clean, 20-25 minutes.