Preheat oven to 375 degrees Fahrenheit. Line a muffin tin with non-stick muffin liners. If you don't have non-stick liners, be sure to spray the liners with a vegetable oil spray so the muffins don't stick. Set aside.
In a high-speed blender, blend the spinach, applesauce, and vanilla until smooth.
Next, add the bananas and eggs and blend again until smooth.
Mix the flour, baking powder, baking soda, and cinnamon in a large bowl.
Add the blender mixture to the dry ingredients and stir to combine, being careful not to overmix.
Scoop the muffin batter into the muffin cups, filling each muffin liner to the brim.
Bake for 18 minutes or until a toothpick comes out clean when pierced in the center of a muffin.