Prepare the Wet Ingredients: In a large mixing bowl, combine the mashed bananas, melted butter, brown sugar, eggs, and vanilla extract. Stir well until the mixture is smooth.
Mix the Dry Ingredients: In a separate bowl, whisk together the flour, baking soda, salt, and cinnamon (if using).
Combine Wet and Dry Mixtures: Gradually add the dry ingredients to the wet ingredients, stirring gently until just combined.
Transfer to Crockpot: Grease the crockpot insert with butter or cooking spray. Pour the banana bread batter into the crockpot.
Cook the Banana Bread: Cover the crockpot with the lid and set it to low heat. Cook for 2 to 2.5 hours, or until a toothpick inserted into the center comes out clean.
Cool and Serve: Let the banana bread cool completely in the crockpot before transferring it to a cooling rack. Slice and enjoy!