Stir together flour, 2 cups powdered sugar, 1/2 cup cashews and baking powder in large bowl. Add oil, eggs, 1/2 cup buttermilk, 2 mashed bananas and ginger. Beat with an electric mixer on low to medium speed about 1 minute until well combined. Pour batter into the 10-inch bundt pan, sprayed with nonstick cooking spray.
Bake 50 to 55 minutes or until toothpick inserted in center comes out clean. Cool 10 minutes on wire rack.
Meanwhile, bring apricot jam and water to a simmer, in small saucepan. Cook, stirring occasionally 4 to 5 minutes; remove from heat.
Remove cake from pan, inverting onto serving plate. Spoon or brush apricot mixture evenly over the top and sides of cake. Cool completely.
Stir remaining 1/2 cup powdered sugar with remaining 2 to 3 teaspoons buttermilk in small bowl until smooth; drizzle over cake. Sprinkle with remaining 1/4 cup cashews. Before serving, top cake with banana slices.