1. Lightly coat an 8 x 4-inch loaf pan with baking spray. Place a small rack or 3 or 4 foil balls (see opposite) into a slow cooker.
2. In a medium bowl, whisk together the flour, baking soda, and salt.
3. In a large bowl, with an electric mixer, beat the butter and brown sugar. Add the bananas, applesauce, egg whites, and vanilla and beat on medium speed until combined. Scrape down the sides of the bowl with a rubber spatula. Add the flour mixture and mix on low speed until just combined. Pour the batter into the prepared pan.
4. Place the chocolate chips in a microwave-safe bowl and microwave in 15-second increments, stirring after each, until the chips are melted. Add dollops of the melted chocolate to the top of the batter. Using a butter knife, swirl the chocolate into the batter. Place the pan in the slow cooker on the rack and cover.
5. Cover and cook on high for 21⁄2 to 3 hours, until a toothpick inserted in the center comes out clean.
6. Remove the pan from the slow cooker and let cool at least 20 minutes in the pan before turning the bread out of the pan. Cut into 12 slices to serve.