Line bottom of 3.5 quarts slow cooker with parchment paper. Coat paper and sides of cooker with cooking spray.
Combine sugar and oil in medium bowl. Beat until creamy, about 1 minute. Add eggs and vanilla extract. Beat until well combined. Add bananas and beat until smooth. Add flour, baking soda, and ½ teaspoon salt, stirring to combine. Beat until batter is creamy and well blended. Fold in pineapple and walnuts. Spread batter evenly in cooker.
Cover and cook on high 2 ¼ to 2 ½ hours or until cake is firm and wooden toothpick is inserted in center comes out clean.
Turn off cooker and uncover. Let cake stand 15 minutes. Remove to rack and cool. Wrap tightly in plastic wrap and chill 8 hours before serving. Sprinkle with confection’s sugar, if desired.
Notes
Recipe source: Prevention Guide: Slow Cooker So Easy!
Recipe by Salu Salo Recipes at https://salu-salo.com/slow-cooker-banana-walnut-cake/