Coat bottoms of 2 (9-inch) round cake pans with cooking spray (do not coat sides of pans); line bottoms with wax paper. Coat wax paper with cooking spray; dust with 1 tablespoon flour.
Beat sugar, shortening, and vanilla at medium speed of a mixer for 5 minutes. Add eggs, 1 at a time, beating well after each addition. Lightly spoon 2 cups flour into dry measuring cups, and level with a knife. Combine 2 cups flour, baking soda, and salt, stirring well with a whisk. Combine the mashed banana and buttermilk. Add the flour mixture to sugar mixture alternately with buttermilk mixture, beginning and ending with flour mixture.
Pour batter into prepared pans. Sharply tap pans once on counter to remove air bubbles. Bake at 350° for 30 minutes or until a wooden pick inserted in center comes out clean. Cool in pans 10 minutes on a wire rack; remove from pans. Remove wax paper. Cool completely on wire rack.
Place 1 cake layer on a plate; spread with 1/2 cup Lemon-Cream Cheese Frosting. Arrange banana slices over frosting. Top with remaining cake layer. Spread remaining frosting over top and sides of cake. Chill 1 hour. Store cake loosely covered in refrigerator.
Lemon-Cream Cheese Frosting:
Beat first 4 ingredients at high speed of a mixer about 2 minutes or just until smooth (do not overbeat). Gradually add powdered sugar, and beat at low speed just until blended (do not overbeat). Cover and chill 2 hours.