Preheat the Oven: Set your oven to 350°F (175°C) and line a muffin tin with paper liners or lightly grease it.
Prepare the Dry Ingredients: In a large bowl, whisk together the flour, brown sugar, baking powder, baking soda, cinnamon, and salt.
Mix the Wet Ingredients: In another bowl, whisk the eggs, mashed bananas, oil, vanilla extract, and Greek yogurt until smooth.
Combine Everything: Add the grated carrots to the wet ingredients, then gently fold the dry ingredients into the wet mixture. Stir just until combined. If using walnuts, fold them in at the end.
Fill the Muffin Cups: Divide the batter evenly into the muffin tin, filling each cup about ¾ full.
Bake: Place in the oven and bake for 18–22 minutes, or until a toothpick inserted into the center comes out clean.
Cool & Serve: Let the muffins cool in the pan for 5 minutes before transferring them to a wire rack. Enjoy warm or at room temperature!