Fold the diced bananas, walnuts, granola, and coconut into the batter. Spoon the batter into the paper liners, filling each 1 to the top. Top each muffin with dried banana chips, granola, or coconut, if desired. Bake for 25 to 30 minutes, or until the tops are brown and a toothpick comes out clean. Cool slightly, remove from the pan, and serve.