Preheat oven to 350°F (175°C) and grease or line a 9×5-inch loaf pan.,In a large bowl, whisk mashed bananas, eggs, sugars, oil, and vanilla until smooth.,Stir in flour, baking soda, salt, and cinnamon until just combined. Fold in blueberries gently.,In a small bowl, mix swirl ingredients: brown sugar and cinnamon (add nutmeg if using).,Pour half the batter into the pan. Sprinkle half the cinnamon swirl mixture on top. Repeat with remaining batter and swirl mix.,Use a knife to gently swirl the cinnamon sugar into the batter.,Bake for 55–65 minutes, or until a toothpick inserted comes out clean or with a few moist crumbs.,Cool in the pan for 10–15 minutes, then transfer to a wire rack to cool completely.