Preheat oven to 350°F. Spray a 9x9 inch baking dish or cake pan.
Stir chocolate chips, brown sugar, walnuts, and cinnamon in small bowl until well blended; set streusel aside.
Stir together all purpose flour, baking soda, baking powder, and salt into medium bowl. Beat sugar, butter, and oil in a large bowl until fluffy. Mix in mashed bananas and vanilla. Add flour mixture and blend well.
Spread batter in prepared baking pan. Sprinkle with streusel pressing down a bit.
Bake coffee cake until toothipick inserted in center comes out clean, about 45 minutes. Cool for about 10 minutes and serve.