Preheat your slow cooker on high for 15 minutes, then turn it to low. Grease the insert line with butter or use parchment paper.

In a large mixing bowl, combine the melted butter with the granulated and brown sugars. Whisk vigorously until smooth. Add the eggs one at a time, followed by the vanilla extract.

Stir in the mashed bananas and the sour cream or Greek yogurt. The mixture will look slightly lumpy, which is perfect.

In a separate bowl, whisk together the flour, baking soda, baking powder, salt, and ground cinnamon. Gently fold into the wet ingredients until just combined. Do not overmix.

In a small bowl, whisk together the brown sugar, flour, 2 teaspoons cinnamon, and melted butter until it forms a thick paste.

Pour half of the batter into the slow cooker. Dollop half of the cinnamon mixture on top and swirl gently with a knife. Add the remaining batter, then the rest of the cinnamon mixture, and swirl again.

Cover and cook on low for 4 hours, or until a toothpick inserted into the center comes out clean. Cooking times may vary based on your slow cooker.

Let the bread cool in the slow cooker for 15 minutes, then transfer to a wire rack. Prepare the frosting by beating cream cheese and butter until smooth, then adding sugar and vanilla. Spread on the cooled bread.