Preheat oven to 350° F. Grease loaf pan and set aside.
Prepare the dark chocolate center by melting chopped chocolate and butter in a small pot over low heat or a small bowl in the microwave. Cool slightly. Whisk in egg and powdered sugar. Cover with plastic wrap and refrigerate while you make the banana bread batter.
In a large bowl, combine melted butter, oil, and mashed bananas. Whisk in egg, vanilla, and brown sugar.
Add flour, baking soda, cinnamon, and salt to banana mixture. Mix until just combined.
Pour batter into prepared loaf pan. Remove dark chocolate mixture from refrigerator and spoon into the center of batter in dollops. Gently press chocolate into batter, making sure it doesn't touch the bottom of pan.
Bake 40-50 minutes or until a wooden skewer inserted into the center of banana bread section comes out clean.
Cool 15 minutes in pan before removing.