Prepare a 12 cup muffin well with baking spray or baking papers.
Preheat the oven to 350 F.
In a medium sized mixing bowl, whisk together the flour, cinnamon, baking powder, baking soda, and salt. Set aside.
In a large mixing bowl, mix together the sugar, mashed bananas, pumpkin puree, eggs, greek yogurt, melted butter, and vanilla extract.
Add the flour mixture to the banana pumpkin mixture and gently fold in with a rubber spatula. Be careful not to overmix, combine until just barely mixed together.
Evenly divide the muffin batter between the muffin wells in the pan, filling each about ¾ full.
Bake for 18-25 minutes, or until a toothpick inserted in the center comes out clean.
Allow to cool in the pan for at least 10-15 minutes before removing.