Preheat the oven to 350 degrees.
Line 20 plus muffin cups with paper liners. Sift the flour, sugar, baking powder, baking soda, and salt into the bowl of an electric mixer fitted with the paddle attachment. Add the melted butter and blend. Combine the eggs, milk, vanilla, and mashed bananas, and add them to the flour-and-butter mixture. Scrape the bowl and blend well. Don't over mix.
Fold the diced bananas, walnuts (optional), granola and coconut into the batter. Spoon the batter into the paper liners, filling each one to the top. Top each muffin with granola or coconut, if desired. Bake 25 to 30 minutes, or until the tops are brown and a toothpick comes out clean. Cool slightly, remove from the pan and serve.