Preheat oven to 350F. Coat a 8 or 9-inch round or square cake pan with butter.
- To prepare cake, beat butter until fluffy. Add sugar and beat well. Add eggs, one at a time, and vanilla; beat well. Add flour and salt; beat until just combined. Stir in banana and cooked oatmeal.
- Spread batter in pan. Bake about 35 minutes. Remove cake from oven. Heat broiler.
- To prepare topping, combine all ingredients. Spread over warm cake. Place under broiler and broil until browned and bubbly, about 4 minutes.
