Grease the inside of a 6-quart slow cooker and line it with parchment paper, leaving an overhang on the sides for easy removal. This helps to prevent sticking and makes serving easier.

In a medium bowl, whisk together the flour, baking soda, and salt. Set aside.

In a large mixing bowl, beat the melted butter and 3/4 cup granulated sugar until creamy. Add the eggs one at a time, mixing well between additions. Stir in the vanilla extract and sour cream or Greek yogurt until just combined.

Gently fold in the mashed ripe bananas. Do not overmix to keep the bread tender.

Gradually add the dry ingredients to the wet mixture, mixing only until just combined. A few streaks of flour are fine.

In a separate small bowl, beat the softened cream cheese with the 1/4 cup sugar, egg yolk, and vanilla until smooth and fluffy.

In a tiny bowl, mix the 2 tablespoons of sugar and 1 teaspoon of cinnamon for the swirl topping.

Pour about half of the banana bread batter into the slow cooker. Dollop the cream cheese filling over the batter. Gently swirl it a few times with a knife or spatula, avoiding the bottom. Pour the remaining batter on top. Sprinkle evenly with the cinnamon sugar topping and swirl gently into the top layer.

Cover the slow cooker and cook on LOW for 3-4 hours. Check for doneness after 3 hours by inserting a toothpick into the center (avoiding the cream cheese); it should come out with moist crumbs. If browning too much, tent with foil.

Let the bread cool in the slow cooker for 15-20 minutes, then use the parchment to lift it out onto a wire rack. Cool completely before slicing for clean cuts.