Allow butter and eggs to stand at room temperature for 30 minutes. Grease and lightly flour a 12 cup bundt pan.
Preheat oven to 350 degrees.
Combine flour, baking powder and salt in medium bowl. Drain pineapple tidbits, reserving 1/4 cup juice. Combine reserved pineapple juice and buttermilk in small bowl.
Beat butter in a large mixing bowl on medium to high speed for 30 seconds. Gradually add sugar, a 1/4 cup at a time, beating on medium speed until well combined. Add eggs, mashed banana and vanilla extract and beat well. Alternately add flour mixture and buttermilk mixture, beating on low after each addition just until combined. Stir in chocolate chips and walnuts. Gently fold in drained pineapple tidbits, strawberries and chopped banana. Spread batter into prepared pan.
Bake for 60 - 65 minutes or until a wooden toothpick inserted near center comes out clean. Cool cake in pan on wire rack for 20 minutes. Remove from pan and cool completely on wire rack. Drizzle cake with chocolate glaze and sprinkle with remaining 1/4 cup walnuts. Cover and refrigerate at least 2 hours before serving.
FOR CHOCOLATE GLAZE: Heat 3/4 cup chocolate chips, 3 tablespoons butter and 3 tablespoons light corn syrup in a small saucepan over low heat stirring until chocolate melts and mixture is smooth. Use immediately.