Preheat oven to 350 F and grease a muffin tin with baking spray.
In a medium sized mixing bowl, whisk together flour, cinnamon, baking soda, and salt. Set aside.
In a large mixing bowl, cream butter and sugar with an electric mixer until fluffy, about 3-4 minutes. Then add egg whites, greek yogurt, and vanilla. Beat until thick.
Mix in 1/3 of the flour mixture at a time, mixing at low speed until combined. Then gently fold in the bananas and chocolate chips.
Pour the batter into the muffin tin and bake on the center rack for 30 minutes. At the 25 minute mark, check your muffins with a toothpick to see if it comes out clean. Let the pan cool for at least 15 minutes before removing the muffins.
Notes
If using frozen bananas, mash them in a fine mesh strainer over the sink and let the excess liquid drain while prepping the ingredients.
Store muffins in an airtight container lined with a paper towel.