Preheat the oven to 350°F (175°C) and grease a muffin tin or line with muffin liners.

In a large mixing bowl, whisk together the dry ingredients: flour, sugar, baking soda, baking powder, salt, and cinnamon.

In another bowl, combine the wet ingredients: mashed bananas, crushed pineapple, vegetable oil, eggs, and vanilla extract. Mix until well combined.

Pour the wet mixture into the dry ingredients and stir gently until just combined. Do not overmix.

If using, fold in the chopped walnuts and shredded coconut.

Spoon the batter into the prepared muffin tin, filling each cup about 2/3 full.

Bake in the preheated oven for 18-20 minutes, or until a toothpick inserted into the center comes out clean.

Allow the muffins to cool in the tin for 5 minutes before transferring to a wire rack to cool completely.