Preheat the oven to 350 degrees.
Lightly spray a muffin tin with cooking spray and if not using nonstick, line with paper or silicone cups. Set aside. In a large bowl, whisk the flour, sugar, baking powder, and salt together and set aside.
Mash the banana really well using a fork or potato masher and set aside. Make a well in the flour mixture and pour in all of the remaining ingredients. Stir until just combined. Spoon batter into cups ¾ full and bake until a toothpick inserted comes out clean, about 15-25 minutes (bake time varies on cranberry size and their natural moisture). Immediately transfer the muffins to a wire rack and let cool.