Preheat oven at 425℉. Line a 12-cup muffin tin with paper liners.
In a large mixing bowl, mash the bananas until smooth with a fork. Mix in wet ingredients: melted butter, Greek yogurt, vanilla, and eggs until fully incorporated. Once mixed, gently stir in coconut and brown sugar.
Add in flour, baking powder, salt and baking soda. Gently fold together until batter is combined.
Coconut Streusel
In a separate small bowl combine flour, brown sugar, coconut, and cinnamon.
Once ingredients are well combined, slowly pour in melted butter while stirring together. Use a fork or small spoon to mix until the streusel topping is a slightly sandy texture.
Once topping is complete, pour muffin batter into lined muffin tin. Sprinkle streusel over the muffins, dividing evenly.
Bake
Bake at 425° for 5 minutes, then decrease temperature to 375° and continue baking for an additional 20 minutes or until a toothpick inserted into the center of a muffin comes out clean.