Preheat oven to 350 degrees, coat pan with cooking spray.
Combine sugars and oil in a bowl, beating at medium speed with an electric mixer. Add banana, mix well. Add eggs, one at a time, beating after each addition. combine flour and soda, add a small amount to sugar mixture. Add a small amount of milk to mix. Alternate mixing in flour and milk into sugar until well blended. Stir in vanilla.
Reserve 1 1/2 cups of batter and set aside. Combine 1 cup of batter with chocolate syrup and 2 tbs cocoa. Stir well.
Pour remaining light colored batter into cake pan. Spoon darker batter on top. Pour reserved light colored batter over darker batter.
Bake for 45 minutes or until tooth pick comes out clean. Cool in pan 10 minutes, remove from pan and cool on wire rack.
Combine powdered sugar with 1 tbs milk and 1 tbs cocoa, stir well and drizzle over cake.