Preheat the oven to 350°F (175°C) and line a muffin pan with muffin liners.
Add bananas, spinach, eggs, honey, milk, coconut oil, and vanilla extract to a blender and blend until smooth.
In a large bowl, whisk together flour, baking powder, baking soda, cinnamon, and salt.
Pour the blended mixture into the dry ingredients and stir gently until combined. Do not overmix.
Divide the batter evenly into the prepared muffin cups.
Bake for 18–20 minutes or until a toothpick inserted into the center comes out clean.
Allow the muffins to cool slightly before serving.