Prep the Slow Cooker: Grease the inside of your slow cooker with butter or cooking spray. Place a slow cooker liner or parchment paper inside for easy removal, and grease the liner or paper as well.

Mix Wet Ingredients: In a large mixing bowl, mash the very ripe bananas until smooth. Add the melted butter, eggs, sour cream or yogurt, and vanilla extract. Stir until well combined.

Prepare Dry Ingredients: In a medium bowl, whisk together the flour, granulated sugar, baking soda, and salt.

Combine and Form Batter: Gently fold the dry ingredients into the wet ingredients until just combined. Do not overmix.

Make Cinnamon Swirl: In a small bowl, mix the brown sugar and ground cinnamon. Stir in the melted butter to form a thick paste.

Assemble in Slow Cooker: Pour half of the batter into the prepared slow cooker. Drop spoonfuls of the cinnamon swirl mixture on top, and use a knife or skewer to gently swirl it into the batter. Pour the remaining batter over the top, and swirl in any remaining cinnamon mixture.

Cook: Cover and cook on HIGH for 1.5 to 2 hours, or until a toothpick inserted in the center comes out clean or with a few moist crumbs. Note: Cooking times vary by crockpot; start checking at 1.5 hours.

Cool and Frost: Remove the liner carefully and let the bread cool in the liner on a wire rack for at least 30 minutes. Meanwhile, prepare the glaze by beating the cream cheese, softened butter, and vanilla until smooth. Gradually add powdered sugar, then milk until desired consistency. Spread or drizzle over the cooled bread.